Unsure what happened, but the game almost broke my android. Had just gotten the knight Aria, then I was grinding the runes... I think something glitched while I was finishing redoing rune 11 or 12 because I saw it flash to a scene for a split second before taking me back to the tower, but then it was like a memory leak became a tidal wave. Phone suddenly started lagging even after I closed the game and lost an hour of progress because I couldn't save due to it lagging, and it was making my phone rapidly heat up because of just how much it was trying to keep up with whatever happened. Not sure what triggered it, sadly... but that was a really bad glitch.
Had to close the app, clear the background processes, and restart my phone to fix the lag even after closing the app.