Downloaded the big update just two days ago. Since then, trying to run Halo in fullscreen has caused a weird glitch to occur after launch where the game itself appears to be in it's regular state, but is shifted upwards and slightly out of bounds on my 16:9 1080p monitor, and for whatever reason, my taskbar is still shown slightly at the bottom of my screen, halfway obscured by the borderless Halo window.

After several hours worth of troubleshooting, I figured out the issue is linked to "Fullscreen Optimizations" in the program's compatibility settings. After disabling Fullscreen Optimizations and applying the changes, the problem was solved, and Halo now behaves properly, as it did before the update.

Just posting this here in case I'm not the only user running into this problem.