To be on the safe side: whatever you have in your Stash that you want to be transferred to non-season, put it in your inventory instead.
This is only for those affected by premature season end from 2 weeks ago that decided not to do account rollback.
Asia server has this issue, that whoever was affected by the season “reset” 2 weeks ago and chose to continue playing with empty Stash, reset Altar etc, did not get season mail after todays season end.