Hey TheJamsh,
I tried testing your issue with different types of blank projects following with your reproducible steps, but was unable to see what you are reporting.
Can you reproduce this in a new blank project?
Also, try closing all of the applications aside from the Engine and see if they could be affecting the issue as well. Have you set the resolution in code somewhere for your project? This could be clamping the overall fullscreen effect of your game, and displaying it improperly on your monitor.
Let me know what you discover and if you have further questions.
Thank you,