The file got removed most certainly while using rsync - rsync does not copy hidden files under all circumstances (I wasn’t aware of this behavior either, but see here: https://www.baeldung.com/linux/rsync-and-hidden-files)
I am glad that the error is resolved, but the steps you mention here shouldn’t have fixed that, so either you followed my suggestion above in one way or the other, or you created said folder “.stfolder” manually, which would also work.