congrats, you disproved nothing i said? 
heck you just specified your own issue, “game reverting stash to pre expansion state” - unlike OP however you didn’t say you tried uninstalling DLC etc “messing with files”
and there can be multiple guesses to why you caused this, cloud, antivirus, save progress reversal (like alt+f4 exiting), corrupt save file so game uses the backup
do we get bonus points for no caps?