Hello,
I use Linux as my daily OS but still really like mIRC, so I always run it inside of Wine.
Since the update to 7.74, whenever someone sends me a private message and this causes a new query window to open, mIRC becomes completely unresponsive and hangs. The CPU usage also goes to a very high percentage.
If I open the query window first before they start talking, there is no problem. Also, the message that causes the issue is still saved to the log, but any messages after that aren't.
Just to be certain it wasn't something about my config, I spun up a clean Linux VM, installed Wine and mIRC and tried it there, and the exact same thing happened.