Thanks Tseegi (.
It's sporadic. I'd say it happens to me maybe once a week in the last month, but has happened yesterday and today.
Reconnecting always 'works' from the connection's perspective, but the connection always appears connected from this view anyway.
Basically you can re-connect times, and then if it doesn't properly work it'll still show the warning sign, but then randomly one will seem to work properly, the warning sign will turn back into the blue toggled bar and the same chat will recognise the connection again