Because all the sudden, I can't get logged in.
I get the login box and it lets me input my username and password into the fields, but when I click the login button, it's like it just doesn't take. I get a visual cue – the outline of the button changes color – but after that, the phone browser treats it like a piece of text: tries to select it for copying and so on.
I tried doing the least drastic form of cache clearing, and that made no difference. I'm wondering whether AO3 changed something underlying the login.