Intermittent issue with v7.63, it doesn't happen with every windows
Sometimes, a window will stay as the active/showed window even if you try to change to another window (channel, status, private message, etc).
Workaround is to close that window or to minimize it, switch window and then switch back to maximize it. Using tile modes will also prevent the issue from happening.
Sometime it'll even make mIRC freeze completely for a few seconds.
No error message unfortunately, it does it on both Windows 10 Home and Pro with all the latest updates installed (tested on 2 PCs).