Bugged resolution in Fortnite competitions

My monitor is ultrawide with a standard resolution of 2560x1080, but when I watch a replay in the compete tab or even play a tournament, I'm forced to change it to 1920x1080 to remove some black borders on the sides of the monitor.

In normal matches and replays, the resolution doesn't change (it stays at 2650x1080). Could someone help me?