If you have all hardware plug-ins (which, by the way, you do), game breaks when you open chest to get another. No real way around this, gotta start over.
There IS a bug where if you quit the game while at the shop, you get sent back to previous tile when you Continue from that same save.
Haven't tested it, but in the future, if this happens and you had another possible tile to choose instead of the chest, you can try seeing if that exploit applies here as well. Otherwise, see above.