It seems to be servers that run countdowns to game start.
If I make it into game when map changes before countdown reaches zero then it's OK.
If the game has started before I can join I get bombed out.
Any Ideas how to fix it?
In the case of RN|OSP, we also were
plagued by this problem (clients randomly disconnect after a new map is loaded with log message was "ERROR: cl.snap.serverTime < cl.oldFrameServerTime"). We came to the same conclusion: the problem occurs if the client cannot load the new map within the specified warmup phase. Our solution was to disable warmup (g_dowarmup "0"). Alternatively, we could have set the length of the warmup phase to a bigger value (g_warmup "15").
Talk to the server's administrators about this problem. If that is not an option, your only choice is to speed up the loading of maps by your client. Buying memory might help. You could also follow the above advice of deleting maps/pk3 files of your ~/.openarena/baseoa directory that you don't play very often (move them temporarily to a backup folder to test the effect).