All three have some timers/threads error close to the end.
I restart KStars in the morning to finish remaining sky flats and it can do 5 to 20 of them before crashing again. I ran it under ekos debugger with a hope to get some more details.
Bonus question, maybe unrelated. One night it was able to stay all the way until the morning and captured half of planned sky flats. See log_20-15-52.txt. But it did not adjust the flats exposure! Several first files were OK, next are totally blown up as expected.