Dmitry Knyaginin <d.knyaginin@gmail.com> writes:

> By the way, I have started to test my theory that the bug has to do with
> the file size, but so far I have not been able to reproduce the bug.

Another guess about your case: I have experienced deleted parts of
buffer and lost history when using undo-tree. Do you happen to use it?

Best,
Ihor