Not sure if this is reproducible but saw a test failure in Stackage Nightly:
Test suite failure for package distributed-process-supervisor-0.2.4
Child Stop Exceeds Timeout/Delay (Becomes Brutal Kill): FAIL (5.58s)
tests/TestSupervisor.hs:679:
expected: DiedException "exit-from=pid://127.0.0.1:38907:0:5227"
but got: DiedException "killed-by=pid://127.0.0.1:38907:0:5227,reason=StoppedBySupervisor"
Use -p '/Child Stop Exceeds Timeout\/Delay (Becomes Brutal Kill)/' to rerun this test only.