When I try and log in I get json back like this:
{"succeeded":true,"error":false,"errorMsg":"","strings":[],"redirect":true,"redirectUrl":"/register-user?target=%2FTalk%2Fsite_stuff%2F3699080-Cant-log-in-on-the-app","formElementNames":[],"formElementErrors":[]}
I had an account but it didn't recognise that (I pasted the redirect urls into my url bar) so I went through registration, for every step when I submitted a form it returned a json not the page itself. On the final registration page it failed due to "Invalid Email" so I edited the POST request and added an email (nothing was in there) which was different from the one I tried to register with (out of curiosity). This successfully completed registration and my confirmation email came to the original email I tried to register with not the one I added to the POST request.
No idea if this sort of thing is happening to anyone else. I'm using Firefox on MacOS if it helps. I can now login with safari with this account.