This is the second time I've had the problem.
The flour has gone all gloopy and like thick cooked batter on top of the casserole.
Did I put too much in?
I cooked it for a few minutes with the veg. Last time I made it I cooked it in with the meat. The whole thing went in the slow cooker.
The recipe said 4tbs of flour, but mine were pretty heaped - and I think I added an extra one as I was planning to put loads more veg in and thought I'd need more stock - but then didn't need the extra stock in the end.