Basically since the recent change by ZOS to intoduce "some FPS control" I have noticed when my char stands still for a while like when at a craft station, provisiong, alchemy etc then the FPS is reduced to 25 - 31 and is locked at this amount unless I relog or sometimes it recovers after about 5 minutes of fast moving activity including maybe combat but cant be certain on the time exactly.
My normal FPS is about 90 is and when it drops to this low number of < 31 it makes the game very jerky and not nice to play.
Sometimes i get my FPS to max for my setup (see below) and its so nice I just wish to not be penalised for spending a good amount of RL money to get a computer setup that can play the game with clear and flowing graphics.