Crash saving score with system divider selected
1) load attached score, which has system dividers enabled in Format / Style / System
2) make any change
3) click one of the dividers to select it
Result: crash (if you don't see this, try opening Timeline, since that's where the crash happens, even though I don't have it open at the time)
Although crash happens in Timeline code, it's not really the fault of that code. Selection is bad. There is one element in the list but it'ss garbage, presumably because the selected divider was deleted and re-generated after the save.
BTW, it's an open question as to whether dividers should be selectable. I had wanted to reposition one, but this doesn't seem to have survived the save (which did complete). This used to work, though - see https://github.com/musescore/MuseScore/pull/2135. I'll file that separately.