Landscape Mode window resizing itself

Sorry if this is the wrong place to post this but I need some help. I’m not entirely sure what’s happening with my Landscape mode but whenever I use it, it does this weird glitch. It seems to resize itself repeatedly and very rapidly. I put a video in here to show what’s happening.

Any help or insight to what’s going on would be great. I really want to get back into UE and create some awesome landscapes again so fixing this is my top priority. Thanks.