Just got a 9520 with the i7 and I have an issue that has shown up a couple times here with older generations, but nothing in fixes it. Youtube 4K and locally stored 4K H.265 video lags significantly, with tons of dropped frames. I noticed that task manager shows the "Video Decode" and "Video Processing" taking nearly 100% on the Iris Xe (my wife's Yoga 9 with a U-series i7 and Iris Xe shows only <10% usage). I can get it to go away sometimes on restarts or reinstalling graphics drivers.
I also noticed in HWinfo (separate app for looking at hardware stats) that when this occurs, the iGPU seems to get stuck at 99MHz. When it doesn't happen, the iGPU scales between 100MHz and 800MHz.
All the latest drivers here. Killer priorization disabled. Feels like a software issue, but one that has persisted over multiple generations (I see people all the way back to 9560 with this issue)? Maybe I have a bad CPU that is randomly locking the GPU clocks at 100MHz?