Getting stuck when typing / Losing app focus?!

Hello,

There's something really weird happening since I installed Mojave (fresh install) last week. I will try to explain what it's going on:

1) I'm using Safari as an example, but it happens to all apps.
2) I switch the focus to another app (command + tab)
3) Then I switch back to Safari
4) I try to type something on a text field or even copy + paste something. It doesn't work and I hear the "Funk" alert sound (go to System Preferences > Sound and you can hear the sound I'm talking about).
5) Switch to another app and go back to Safari.
6) Now I can type again.

This happens MANY times during the day. It's extremely annoying and frustrating.

It feels like the current app (Safari in this example) is not the "focused" app, even though it is. I can still scroll the Safari page, select elements on the page, but if I try to use the keyboard, I get that sound. This is a fresh install and I haven't installed any app that could be causing this issue.

Has anybody seen this weird behavior before?

Thanks