This bug was reproduced on CFME-5.9.0.20/RHV-4.1.8.2,
by power off VM on RHV side, and generating the error in evm.log, mentioned in the bug description, that followed the USER_STOP_VM event.
On CFME-5.9.0.21/RHV-4.1.8.2, this error no longer exist.
Event USER_STOP_VM is handled, and also displayed under VM Timelines Power events.