From the marketplace page of the Map and Card Deck addon: Important Notice:
The Waterdeep: Dungeon of the Mad Mage - Map & Card Deck
Addon is not designed to be added into the core Dungeon of the Mad Mage
adventure module, as these elements already exist within the module.
Attempting to import them into the core module will result in your
current maps being overwritten by the addon's maps. The addon is for people that own the physical product and just want the maps/cards to cut down on prep time. Hopefully, if you remove the addon from your game it will return to normal. If not, you may need to just start over.