copling desync

[Tsumiki129]

hi me and my friend have been playing with mp and a friend have been experiencing a de sync with copping and decoupling trains at times we have experienced it about 3 sepret times were my freind would couple up and move them but on my end (the hoset) they have failed to couple or a similar one is wen they are decoupled they dont decouple but visual are on both host and client both in vr and out of vr

[AMacro]

Hi @Tsumiki129

Next time it happens, can you please:

1. Generate a bug report (bring up the menu and use the bug report feature)
2. Upload the bug report to this issue
3. Get the other players to generate a bug report and uplod to here (or you can upload for them)

[stroebs]

DV_BugReport_2026-02-10_00-07-30-CLIENT2.zip
DV_BugReport_2026-02-10_00-07-26-CLIENT1.zip
DV_BugReport_2026-02-09_22-07-27-HOST.zip

CLIENT2 Screenshot:

CLIENT1 Screenshot:

HOST Screenshot:

BEHAVIOUR:
CLIENT1 did decouple of car CBK504 from L-018 using F4 menu, HOST shows the car is mechanically coupled but hose is not, and cock is not closed. Clients both show fully decoupled.

Based on the log, it looks like the coupling interaction either wasn't received, or wasn't handled correctly by the host. There were multiple successful coupling events over the play session and this happened more than once over the last play session (log also included), with the exact same behaviour.

Network-wise, HOST is in the UK, both CLIENT1 and CLIENT2 are in South Africa with about 170ms latency from HOST. They have about 10ms between each other.

[stefanenthoven]

I think the issue is with the check that no one else is interacting

Host log:

[Multiplayer] [22:54:14.455] [Debug] Common_ReceiveCouplerInteraction() couplerNetId: 10, coupler is front: True, flags: Start, HoseDisconnect, CockClose, UncoupleViaUI, otherCouplerNetId: 0, otherCoupler is front: False
[Multiplayer] [22:54:14.455] [Debug] Common_ReceiveCouplerInteraction() [L-056, 10], coupler is front: True, flags: Start, HoseDisconnect, CockClose, UncoupleViaUI, otherCouplerNetId: 0
[Multiplayer] [22:54:14.455] [Debug] 11 Common_ReceiveCouplerInteraction() [L-056, 10], coupler is front: True, flags: Start, HoseDisconnect, CockClose, UncoupleViaUI, chainInteraction: False


[Multiplayer] [22:54:17.745] [Debug] UICouplingHelper.HandleCoupling(L-056, True)
[Multiplayer] [22:54:17.745] [Debug] UICouplingHelper.HandleCoupling(L-056, True) coupler is front: True, otherCoupler: CBK685, otherCoupler is front: False, action: Start, HoseConnect, CockOpen, CoupleViaUI
[Multiplayer] [22:54:17.746] [Debug] [Client] SendCouplerInteraction([Start, HoseConnect, CockOpen, CoupleViaUI], L-056, CBK685) coupler isFront: True, otherCoupler isFront: False
[Multiplayer] [22:54:17.746] [Info] [Client] Sending coupler interaction [Start, HoseConnect, CockOpen, CoupleViaUI] for L-056, Front

[Multiplayer] [22:54:17.794] [Debug] Server_ValidateCouplerInteraction([[Start, HoseConnect, CockOpen, CoupleViaUI], L-056, 10], 1) isFront: True, frontInteracting: True, frontInteractionPeer: 2 (Phoenix, ad0c3ab2-f674-454b-9519-28ae0778585f), rearInteracting: False, rearInteractionPeer: 
[Multiplayer] [22:54:17.794] [Debug] Server_ValidateCouplerInteraction([1345, L-056, 10], 1) Failed to validate!
[Multiplayer] [22:54:17.794] [Debug] [Server] OnCommonCouplerInteractionPacket([1345, L-056, 10], 1) Sending validation failure
[Multiplayer] [22:54:17.846] [Debug] Common_ReceiveCouplerInteraction() couplerNetId: 10, coupler is front: True, flags: NoAction, otherCouplerNetId: 0, otherCoupler is front: False
[Multiplayer] [22:54:17.846] [Debug] Common_ReceiveCouplerInteraction() [L-056, 10], coupler is front: True, flags: NoAction, otherCouplerNetId: 0
[Multiplayer] [22:54:17.846] [Debug] Common_ReceiveCouplerInteraction() Interaction rejected! [L-056, 10]
[Multiplayer] [22:54:17.846] [Debug] Common_ReceiveCouplerInteraction() Unable to return to last state! Disabled

Client log:

[Multiplayer] [22:54:14.274] [Debug] DisconnectAirHose(CBK685, False)
[Multiplayer] [22:54:14.274] [Debug] [Client] SendHoseDisconnected(CBK685, False, False)
[Multiplayer] [22:54:14.274] [Debug] DisconnectAirHose(L-056, True)
[Multiplayer] [22:54:14.274] [Debug] [Client] SendHoseDisconnected(L-056, True, True)
[Multiplayer] [22:54:14.274] [Debug] UICouplingHelper.HandleCoupling(L-056, True)
[Multiplayer] [22:54:14.274] [Debug] [Client] SendCouplerInteraction([Start, HoseDisconnect, CockClose, UncoupleViaUI], L-056, ) coupler isFront: True, otherCoupler isFront: False
[Multiplayer] [22:54:14.274] [Info] [Client] Sending coupler interaction [Start, HoseDisconnect, CockClose, UncoupleViaUI] for L-056, Front

[Multiplayer] [22:54:17.858] [Warning] Received ClientboundTrainsetPhysicsPacket for trainset with FirstNetId: 10 and LastNetId: 12 with 2 parts, but trainset has 1 parts

dv-multiplayer/Multiplayer/Components/Networking/Train/NetworkedTrainCar.cs

Line 846 in 06c5110

//Ensure no one else is interacting

[stefanenthoven]

I commented out these lines and we had a full evening session with no desync issues. I'm not sure the original reason for checking that no one else is interacting, but maybe it is not necessary.

//Ensure no one else is interacting
//if (packet.IsFrontCoupler && frontInteracting && player != frontInteractionPlayer ||
//   packet.IsFrontCoupler == false && rearInteracting && player != rearInteractionPlayer)
//{
//    Multiplayer.LogDebug(() => $"Server_ValidateCouplerInteraction([{packet.Flags}, {CurrentID}, {packet.NetId}], {player.PlayerId}) Failed to validate!");
//    return false;
//}

Edit:
Thinking about it more, we pretty much only coupled using the F4 menu. The above code might have a use during manual coupling

[Rognar92]

I commented out these lines and we had a full evening session with no desync issues. I'm not sure the original reason for checking that no one else is interacting, but maybe it is not necessary.

Hello, in which file is this file edited and how? I can't find it.

[stefanenthoven]

I commented out these lines and we had a full evening session with no desync issues. I'm not sure the original reason for checking that no one else is interacting, but maybe it is not necessary.

Hello, in which file is this file edited and how? I can't find it.

It's here:

dv-multiplayer/Multiplayer/Components/Networking/Train/NetworkedTrainCar.cs

Line 846 in 06c5110

//Ensure no one else is interacting

You would have to download and edit the source code and then compile it following the build instructions in the repo

[AMacro]

Sorry guys, I missed the replies.

The check for manual coupling is necessary, but using the F4 menu should still allow the coupling to occur. I will have to look into what's going on here

[stefanenthoven]

Yes there is some sort of bug with the interaction check.
We found when playing using the F4 menu, if another player has the car selected and you try and couple, the interaction check does not pass, the server then tries to roll back the coupling action but that has an error and ends in a broken state.
This is easy to reproduce and happens reliably.
By disabling the interaction check, we could play (using F4 menu for coupling) with no issues. I understand it would be needed for manual coupling.

By the way we also experienced another bug where you are driving a train and the brake hose will randomly disconnect applying brakes, but did not find a way to reproduce it or get debug info.

[Rognar92]

Copy-Item : Cannot bind argument to parameter 'Path' because it is an empty string.
E:\Desktop\dv-multiplayer-06c5110a72ba78298f48c5dc862447b9924b0c84\post-build.ps1:25 character:11
+ Copy-Item ($Target) -Destination ("$PSScriptRoot/build/")
+ ~~~~~~~~~
+ CategoryInfo: InvalidData: (:) [Copy-Item], ParameterBindingValidationException
+ FullyQualifiedErrorId: ParameterArgumentValidationErrorEmptyStringNotAllowed,Microsoft.PowerShell.Commands.Copy
ItemCommand

Test-Path: Cannot bind argument to parameter "Path" because it is an empty string.
E:\Desktop\dv-multiplayer-06c5110a72ba78298f48c5dc862447b9924b0c84\post-build.ps1:29 sign:17
+ if (!(Test-Path($GameDir))) {
+ ~~~~~~~~~~
    + CategoryInfo : InvalidData: (:) [Test-Path], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyStringNotAllowed,Microsoft.PowerShell.Commands.Test
   PathCommand``

Please tell me what I'm doing wrong?

[AMacro]

By the way we also experienced another bug where you are driving a train and the brake hose will randomly disconnect applying brakes, but did not find a way to reproduce it or get debug info.

The brake issue I believe is caused by a lag spike. The update I've just released should fix it (appears to have resolved the issue in the testing)

Please tell me what I'm doing wrong?

I suspect you haven't created your own Directory.BuildTargets and checked the paths are correct.

@Rognar92 I've updated the readme with better instructions

[AMacro]

@stefanenthoven

We found when playing using the F4 menu, if another player has the car selected and you try and couple, the interaction check does not pass, the server then tries to roll back the coupling action but that has an error and ends in a broken state. This is easy to reproduce and happens reliably.

Ok, just to make sure I understand, the issue occurs if more than one player has the coupling UI open?

I'm trying to reproduce this, but everything is working, so I think I'm missing something

[stefanenthoven]

Ah, I didn't realise that menu existed. We were coupling using the menu you get when clicking on the train car, as shown in our screenshots from earlier

…

On Sat, 14 Mar 2026, 04:46 Macka, ***@***.***> wrote: *AMacro* left a comment (AMacro/dv-multiplayer#122) <#122 (comment)> @stefanenthoven <https://github.com/stefanenthoven> We found when playing using the F4 menu, if another player has the car selected and you try and couple, the interaction check does not pass, the server then tries to roll back the coupling action but that has an error and ends in a broken state. This is easy to reproduce and happens reliably. Ok, just to make sure I understand, the issue occurs if more than one player has the coupling UI open? image.png (view on web) <https://github.com/user-attachments/assets/66731490-f892-4fbf-a3c5-d9bc6ef92313> I'm trying to reproduce this, but everything is working, so I think I'm missing something — Reply to this email directly, view it on GitHub <#122 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABN5WDHEKRC5K2S7FUULMFL4QTBW3AVCNFSM6AAAAACSCUX7SOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DANJZGI2TMNRSGM> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[AMacro]

@stefanenthoven @Rognar92 @Tsumiki129 @stroebs

Please test the Alpha version and let me know if it does/does not resolve your issue. Note: ensure you are using the Multiplayer.0.1.13.13.zip and not the source zips when installing the mod.

If the issue is resolved and no new issues introduced, I will do an official release.