I should add that this issue seems confined to the Roku platform.. I have Android TV devices, Roku, Firetv..
The app seems to load and play fine on the others. So if you have an old Firetv stick laying around.,you could switch to it in the interim. (ironically, I actually bought a Roku stick a few years ago only for the NFL app since the performance on the other platforms was so awful.)
This is interesting.. because one of the reasons I have a Roku device where I watch football, is because the app experience is superior on the Roku platform, and it generally works better. The difference in user experience was much larger in the past than today.. Today all versions of the app essentially behave the same, but still the Roku platform is the smoothest performer for the NFL app.
By trade I am a systems engineer and deal with this kind of thing often. I understand that things like this can happen. It doesn't mean the design was horrible or there is a glaring engineering defect, but obviously something isn't working.
Fingers crossed it will get fixed soon.
