I bought both of the extensions (hot wheels and blizzard mountain) and sometimes when trying to travel to them I’m getting a message offering me to install the extensions rather than taking me there. When clicking the install I get the message that I already purchased the extension, select the purchased option takes me to the Microsoft store which offers me to buys it as a gift. On the other hand, sometimes it works just fine and I can travel to the extension.
Try to make sure your Microsoft Store App is updated, as there is sometimes issues with verifying you own the game. This tends to happen right after an update, which gets fixed by another update. If that doesn’t work. Maybe try to uninstall the Extension Maps and/or entire game and reinstall. If these don’t work, I would contact Xbox/Microsoft Support.