I've happily had a 2.5 Minion running on a Flow rim. I took the tyre off a few days ago and now can't remount it. The tyre won't lock onto the bead hooks. Even with a tube in, it doesn't 'pop' into place and just drops back into the centre channel when the tube is deflated.
A Schwalbe Nobby Nik locks on fine. What's going on? Any ideas?