I face the same issue with live TV broadcasting in 1080p (TVHeadend). Every few seconds there is an annoying microstutter, I’ve tried several settings including the mentioned advancedsettings in this thread - nothing really helps.
I’ve switched from an old RasPi2 to the S905X (Mediasee N5) today and really thought everything will be much more powerful (as the S905X can play back 4k 60fps) - and I’m a bit shocked. Never had this issue at the same stations on the old RasPi.
If anyone has ideas apart from overclocking the GPU (which I don’t like) … they are welcome.