I did a little work last night.
Basically the map all works fine again but now it's super fast.
Super fast enough for lots of things to happen at once and therefore allow the rest of the game to proceed as normal.
The only things that's a little stuffed is the character animation. I can do a hack to fix it, as it's something I've done before, and then removed. I'd rather get to the root of the problem though and make things work a lot better overall.