I don't know your solution, just some things to try:
1. See if speeding up screen writes makes the problem go away: /fupdate 99
Note that /fupdate doesn't appear to have a mirc.ini setting, so you must do it each time you restart
2. See if exempting the mirc folder from your antivirus can prevent it from slowing down the client's disk accesses.
3. You weren't clear whether you were using. If it's older than 7.52, there was a bug fix that helped against a freeze.
11.Fixed online timer bug that caused mIRC to freeze once a minute the more connected status windows were open.
4. Test whether it happens with a partial setup. If it happens with 22/50, does the problem go away when you kill some of the status windows, or does ithe problem not appear until you've added the Nth status window? etc.