You'll need to make sure the position references for various events are updated whenever you change the background's dimensions! In this case, if you expanded the scene to 192x176, your Replace Tile At Position events are now offset, so you're replacing all the tiles that match the new positions (in this case, it looks like it's grabbing a blank white tile).

Based on what you called out for the junk tiles, I messed around with an updated battle scene of 176x160 (putting a 1 8x8 tile black border around the scene) and the set the camera position (and updated my event position references), and it doesn't seem to use garbage tiles when shaking the screen anymore. It's a good call out, so I'll update the backgrounds for future Quests (I also want to clean up the text box borders so this is a good opportunity for an update).

Let me know if that works!