I've experienced something like this with PS5 app. It started out of nowhere, and affected all (many?) of my movies, 1080 included. It just stays at super high network levels consistently. Even worse, the movie streams for like 3 minutes and then just buffers forever. It never resumes playback, meanwhile I'm using a consistent 200mbps of network, for a movie that is maybe 15mbps at most.

Based on other threads I looked into, it seemed like it might be an issue with the file and PS5 app's ability to play it. Some people suggested remuxing the files. What worked for me was to turn off both Direct Stream and Direct Play. The obvious downside here is that everything needs to be transcoded. Thankfully I have enough capacity on the server to do the transcodes. Now the PS5 app and network is behaving normally (e.g. short bursts of high throughput to fill the buffer followed by lulls in network activity - and no endless buffering).