Yo @WarcraftDevs I wanna run M+ but my key dropped at +18. I can't grind it down to a doable level because I hit an instance cap.
We quickly fixed the underlying issue that caused some players to receive high level Mythic Keystones. Deleting the key and running another Mythic dungeon will grant you a new Mythic Keystone.
As a reminder, the instance cap is hourly.