Howdy!
I wanted to provide an update to this issue. We are aware of the game being stuck loading for the following Solo Adventures: The League of Explorers, Blackrock Mountain, or Naxxramas. The game will either freeze on Loading… or provide an exception crash. This is already under review by our QA and Developers for resolution in a future update. I don’t have an exact ETA but the team is already on the case!