If it doesn’t work in M0, just run a higher key. If I didn’t play m+ on an alt for a week, I always get one in some +15 a week later.
It could also be that you HAD a key, but deleted it. You won’t get a new one until wednesday then. Never delete keys, you can change them (random) at the end of a succesful run, if your key lvl is lower or the same of the succesfully timed dungeon.
I’ve never even had a key on my character this season to delete. My last key I owned was on a Paladin that i’ve not played on for a year.
Also I submitted a ticket to Blizzard, but they just gave me an automated response with the same advice in this thread. I’ve re-opened in hopes a human actually helps me.