It is never acceptable for Sigil to crash. We have tracked down and fixed all that have been reported. Please post a test epub and a set of reproducible steps that cause the crash and we will get it fixed.
Unfortunately Windows does not provide a full backtrace by default to the user.
Perhaps a Windows person can figure out a way to get a real backtrace of your next crash.
Also there are Windows system shell extensions that can cause great instability in all Qt apps like calibre and Sigil. Calibre's website has a list of known problem software in their FAQs. See their link for more info:
https://manual.calibre-ebook.com/faq...s-occasionally
Please verify Sigil still crashes when you disable extensions when booting Windows.
Also verify the issues are not caused by anti-virus software.
Also verify you are not leaving Sigil running with an open epub over multiple days as some Windows security settings will auto delete files in tmp open for more that 24 hours. Either turn off that self cleaning Windows setting or set Sigil preferences to use your own created folder outside of tmp.
Also verify system tmp is not on a networked drive as this can cause file locking issues.
Based on all of my testing Sigil 1.9.20 on linux and macos is rock steady. I assume the same holds for Windows. At least this is the first crash report in quite a while.
If Qt version matters, it is probably a clash with a Qt version in some other app or system extension.