Re the instability, see here, but I was asking about what this particular message meant** rather than about the instability per se.
** I suspect that it means that the Javascript running in my browser has lost contact with the server, lets me continue anyway, but is not able to reconnect when the server comes back (possibly due to a bug / lack of a feature in that JS). However this is largely guesswork on my part; that’s why I was wondering if there was any actual documentation.