I think this may be a bug? I'm in a boss fight and had to built myself into this position due to bad tiles at the time. I think the boss is meant to realise I have no path available and hurt me (plus reset the tiles)?
Correct, the crash occured when I went to place a tile and then tried to put it back (to grab another tile).
It does get a bit easy towards the end, you can end up with so much life that it doesn't really matter if you have to block of large sections of the map.
Maybe a max limit on health might help? It would take a bit to work out the sweet spot for late game difficulty, perhaps around 50
