Opened MSE to find that nearly a third of my cards have a blank text box. Confused, I clicked on one to see what's up, and I can't type into the text box anymore. Whenever I click on one of the cards with the issue or attempt to modify it in any way, I get the following Console error:
Can't convert "no " from string ("no ") to boolean
Edit: After further investigation it seems that the blank cards aren't random - any card that previously included a mana symbol in the text box is now appearing blank - every other card is fine.
Edit 2: After even further tweaking (read: I purposefully created an error in magic-mana-small.mse-symbol-font/symbol-font by deleting a } and rerunning MSE, clicking to Console, and then fixing it again) I managed to solve the issue. Haven't a clue what happened there, but I'll leave this here in case anyone else has a similar problem as a possible fix/workaround.