ingame save invalid when fastforward turning on in gpsp

[hiro1vv]

device: TSP
nextui ver: 6.9.3
SD format: exfat
game rom: pokemon leafgreen fantranslation (based on US rom)
core: gpsp(default)
settings: real-gba.cfg and rewind is on
problem: when FF is on, ingame save sames normal, but when game frozen after playing for hours (saved several times during time), long press power button to force reboot, reload game rom, the save shows much earlier save point. e.g. start playing at total playtime 12:20, frozen at 14:40, during playing saved every 15min, reboot and load save show lastest safe point at 13:45.
things already tried:

1. play and save several times under FF turning off, use menu to quit gpsp, reload game. save point shows latest correctly.
2. move rom and sav file from gba folder to mgba folder, using mgba to play with FF turning on, play and save several times, use menu to quit mgba, reload game. save point shows latest correctly.

why not using mgba: FF on mgba only goes approximately 1.25x, and FF on gpsp goes approximately 2.5x (both setting as max FF speed 2x, don't know how to turn on fps or speed HUD）

update:
after i turning up rewind rewind interval and turn off rewind compression, now mgba can run at approximately 1.5x-1.75x. played for hours, same thing happened: game froze, reboot found recent save point lost. now i suspect the problem is exfat format(TF card quality ok, been playing FF6 without problem) or game rom.