You will need to follow the steps I provided in my first reply, eg. install a clean, portable copy of mIRC, no scripts/DLLS, and so on. You can then run this copy of mIRC to see if the issue is still present.
It would be very easy to make mIRC to freeze repeatedly if you are using scripts that process events on many channels with many users. In addition, some features in mIRC may be processed once or more a minute, eg. the nick colors or highlight feature, and are CPU intensive as they depend on finding matches in nickname lists on all of the channels you are on. If you are on channels with thousands of users, mIRC will need to apply those features/settings to thousands of users once a minute, which takes time.
The first step is to narrow down the cause of the issue. If you can narrow it down to a specific feature, script, etc. this may help you optimize it or at least pinpoint a feature that I might be able to optimize.
