Ah, you've identified a couple more variables you can try elimininating 1 at a time. I doubt passwording with nickserv could cause this problem, but there might be something about the 6 channels that's causing this. Those are 2 things that are different than when you tried joining Rizon. Even if you joined the same 6 channels at Rizon, they wouldn't have the same headcounts.

If you add the following code to the REMOTE tab of the scripts editor, this might give you a clue as to when the freeze is happening, whether it happens before/during/after joining the channels, whether there's 1 big freeze or several freezes, etc.

alias debugline { return $asctime(HH:nn:ss) $1- }
on *:CONNECT:{ debug -i @debug debugline | aline @debug $uptime(server,1) $event $server }
on *:JOIN:#:{                              aline @debug $uptime(server,1) $event $server $chan }