I don't have an answer but I wanted to relay what had to be done for me.
In 2020, the ROKU app was horribly broken. The NFL development people were working to fix the ROKU app (at the time there was conflicting information whether the ROKU app was even supported.. Literally one support page said it was and another page did not list it as supported.) ugh..
Finally NFL support just de-registered all my configured devices, deleted my account and set me up again. After that, things started working - but not very well on the ROKU. I still had issues with performance. I found that the FireTV app worked ok and I had to use it for access to work. Even though I had to use a different device, it worked.
When the 2021 season began, I fired up the NFL apps. The NFL folks had updated the ROKU app and the issues I had in 2020 were gone. Ironically, I found the ROKU app to perform much better than the FireTV app I had to use previously. (hiding scores didn't work etc and there were different behaviors) I used the ROKU exclusively this season, and was very pleased. I even picked up a ROKU stick to use elsewhere in the house since it worked so much better than the other platforms for the NFL.
I am curious if you have another device to compare performance? It is likely the issue is with the NFL app / service and not the ROKU. The NFL support folks were horrible at responding.. so brace yourself. Be very concise and short with your support ticket. They will only read about the first two lines and send a canned response. It's very frustrating.