Strange behaviour with apps

Hi everyone! I just started having a bit of a weird issue. In every app I use (for example even when typing this message), the main window of the app becomes "inactive", like if I was clicking somewhere else, every 10 seconds, more or less, and it lasts for a couple of seconds each time.

I thought I was a problem with the magic mouse or keyboard, but even with them off it still does it. I have never seen anything like it, I don't have any random window going on on any other screen, it's just bizarre...

Could please anyone help?

Thanks