I regularly play on ultra PC for FO4, my gaming rig is enough to handle it so I wont bore you with specs.
The last two times I played my graphics are stuck on low, its is slowly killing me and my immersion!
I recently nexus modded a few texture packs, I uninstalled these to see if they were the issue - they were not. No new changes have happened.
Not matter how many times I select ultra my play is stuck on LOW I know it's low when codsworth is all one color and has zero reflection or shine.