Last night when normal chrome was erroring out, (edit/update: Auth is successful but Chrome cannot successfully load the live video feed for some reason) incognito Chrome was working, then I cleared cookies and regular chrome started working. But I never know if anything I do changes it or if it is just working or not. Yes I am suspicious of the "live game" feeds as others have mentioned in this thread, those have special restrictions sometimes. But I am even NFL GamePass subscriber so I have access to all preSeason games. Which I have wondered could be a complicating factor for my particular situation. But gamePass logins are somewhat separate from normal provider logins. But anyway, I don't know if the chrome browser issues I experience on both macOS and iOS chrome browsers are enough to prove it has nothing to do with ChannelsDVR, but I think it does prove that. AFAIK they are are still using a headless chromium browser or similar to handle the auth for the streams.
Other NFL Blackout information. YES, NFL Blackout rules have been applying to preSeason games from what I have seen. So if a local channel in your area is carrying the NFL preseason game (usually a local CBS or Fox channel, but could be any local network), then the NFL network feed is blocked to you. There is some type of message that does show on the screen, though, it is not the same as a login error or forbidden error....IIRC. I don't think the GamePass subscription or anything else can override this either. So this may make troubleshooting the issues more complicated. I don't profess to be an expert in NFL blackout rules, apologize if any of this info is wrong. It may not matter whether a local station carries the game or not, just the game being in your local area may mean blackouts. there have been some changes in blackout handling over the years. Sold out or Certain % of seats sold for instance was changed at some point.