Resolution decreases dramatically on start with borderless fullscreen

When starting the game with borderless fullscreen enabled, the resolution is significantly lower than it's supposed to be. I play at 1080p, but it looks like 480p. Switching to fullscreen and back in the graphics settings resets it back to 1080p. I do not have any upscaling enabled; I am playing at native resolution. 

This problem first started when I switched to a different graphics preset. Ever since I did this, I have to perform the aforementioned fullscreen switch at the start. 

I feel it should be relevant to mention that I have supersampling enabled on my PC to make some other games more crisp. 

This screenshot is taken at native resolution and accurately displays what my game looks like at the start.