FP2 not joining hotspots, nor falling back to data

I wanted to post this separately from the wifi exclamation mark issue. It may be connected, but it’s a much bigger problem.

I’m seeing no sign-in pages come up for hotspots. So if I’m in the mall, my phone can join a hotspot, loose internet connectivity - it doesn’t fallback to mobile data - and it’s without me knowing (there was already an exclamation mark so there’s nothing new for it to add) and it won’t let me get on the internet because it won’t sign me in. Do hope there is a fix for this. It can’t be just an Android problem because I didn’t have it on my old phone which also ran 5.1. (The only way I have spotted this is when I’ve opened Whatsapp which does then warn me of lost connectivity). I think I may have seen the log in work when mobile data was off.

Can anyone else reproduce this?