OK wait weirdly it fixed itself after an hour (?)
Things that may have worked:
- Settings > General > Date & Time > Automatic Date&Time toggled it off and back on again
- Went to friends / clan / settings and clicked around?
Weirdly, the prompt to retry / reconnect has appeared maybe 100x after so many restarts that did nothing. :] Maybe the issue was just temporal or transient.
Anyways, thanks all!