Yikes. I had to stop using JetBrains software for similar reason (their autosave effectively conflicted with external git usage). This is inexcusable to me but to each their own.
Don't they have an auto-save setting that you can turn off?
Yes, but I think it still behaved weirdly with external changes. It's been a few years now, maybe it discarded any unsaved changes and just re-read the version from disk, or maybe it auto closed any editors for files that didn't exist after a branch change. Awkward behavior like that. VSCode and Sublime Text are much better in this regard.