I see posts on boards I've subscribed to in the notification window but clicking on any gives me a warning similar to this:

Which suggests it's a login issue.
Logging in just gives me this:

There's obviously no actual problem with my login (as I'm posting this from the same phone via the web interface).
No other TapaTalk forums are affected for me so doesn't seem like an app issue.
Been like it for a couple of days - anyone else?
Johnny