Just installed Windows 10 - alt+tab stops working a few seconds after boot

Yesterday I inserted a brand new SSD drive into my laptop and installed Windows 10 Enterprise. Most things work ok, and I am getting used to the new interface (coming from 8.1). However, alt-tab does not work. The only result of pressing the combo is that the current window loses focus.

I tested right after a boot and it works briefly, but then stops having any positive effect after a while. Win-Tab works but the alt-tab shortcut has long ago become muscle memory so I want to keep it. :)

I am thinking that there is some sort of software I installed that caused this since it works for a while after boot. AquaSnap Pro has some keyboard shortcuts but none that go near alt-tab as far as I can tell. Greenshot also has some but should not block it either. I am not currently ruing AutoHotKey even if I want to once I figure this out.

Is there a way to see what "happens" in the OS when you press a hotkey like this, and figure out which application "eats" the event?

Any other tips on getting my alt tab back?