@DiapDealer - yeah these sorts of issues can be a royal pain to track down. If we can ever replicate then there is hope for fixing it - attaching a debugger as a starting point to find out what it was trying to do at the time. If necessary I can dive into crash dumps with the SDK debugging tools, though only as a last resort as it is a massive time sink.
There are of course sometimes issues for some users with their environment, like the KDE related issues with Qt for instance. Wacom mouse problems, antivirus, Qt versions and all those other weird and wonderful things that we can do little about as an application developer.
With all that said, a vast number of crashing scenarios have come down to bugs in Sigil code, be it not handling exceptions during cross threaded operations, race conditions or by not disposing of memory/resources correctly.
We will certainly keep testing and of course if others notice the same issue do please report it.