timo
I think you onto something regarding "focus timer"
I disabled "sync with time tracking" and played around with it for a while, opening and closing, starting, stoping, resuming ... and it Appears to be all working when "sync with time tracking" disabled.
Also when I Enabled "sync with time tracking" again, there also seemed to be strange issue when then trying "resume work" where it didn't crash, but it also didn't quite start .. almost like it was paused, and I had to then click start. And "rounded off" was disabled.
Another thing which probably is Not related, but when I had WH set to start on windows start, it seemed to automatically start timer...