Dungeon of the Mad Mage: All tokens disappeared from all maps?

I'm just starting to set up and after making a bunch of changes to the game and importing the characters, I realized that all of the tokens had vanished from my maps. They're still on the token page, but none of the map pages. I've already created a new game (I didn't have much to redo), but if this happened half way through the campaign, it would be a huge problem. Can anyone tell me what happened and how to avoid it in the future? Unfortunately, I don't know what I did just before it happened. The biggest change I made was swapping sheets (from default to 5e Shaped), but I can't imagine that would delete tokens.

Check the settings for the GM layer opacity (in the layer flyout menu). If that somehow got set to zero, it could make all the GM layer tokens appear to disappear. If they do actually diasppear mid-campaign, you can use the Transmogrifier to pull in replacement maps from a backup copy of the Mad Mage game.

I had no idea about the transmogrifier. That solves my problem, and just made my entire life easier lol. Thanks.