I have also checked task scheduler for any culprits and I have found none executing every 30th minute and I also checked "Last Run Time". There's so many scheduling tasks so I ran a powershell script after "Last Run Time" and none stood out.
I've tried to find a tool that would allow me to see if any application changes focus to another application but no luck. There's only focus logging applications and that wouldn't be very helpful and event viewer doesn't give much either.
I noticed that the focus isn't exactly every 30th minute, this time it was a around 5 seconds late.
I really don't want to switch IRC client. I've used mIRC since late 90's and I've loved it since (and written tons of scripts - none executing timers every 30th minute though 😆) but this is just purely annoying. I don't know if it's something conflicting with my installed applications I have running but I've used the same applications for like, forever... I also can't understand why mIRC is getting focus even if it would have been from a third party software.

I did update the client not long ago and it was after that the problem started so that kind of gives me the impression that the newer version(s) gave me problems.
I guess I could revert to older versions and give it a try and give feedback though. I guess I can do a "debug" when I do have time though.