Full screen keeps minimizing

I have a 13 inch 2016 Macbook Pro (macOS Sierra 10.12.4) and today I started experiencing some sort of bug. Whenever I try to watch a video on full screen (Quicktime or even Netflix on Safari), the video keeps minimizing and moving to the top left corner of the screen. It will happen like every 3 seconds (it minimizes, then it goes back to full screen mode, and after a few seconds it happens again). Has anyone ever experienced this?

Here's an example (using Quicktime):

https://youtu.be/Vo511XdsCAA

Thanks!
Luisa