Like what you see is 480 or the option is missing?
On my T-Mobile variant (S7 Edge) I can do 1080p using the same video on wifi or mobile data (all shown below). I closed the app, shut wifi off, and went back with mobile data to ensure.
Yeah I have been having the same problem lately. For me this problem started a few days ago and I went back to watch videos I knew were in 1080p quality and they were now being limited to 480p. But some other videos are working fine at 1440p and 1080p resolution.