One thing I have noticed, is that the Z7+ become hot (very hot) when the buffering starts. Could it be this be the explanation ? Critical temperature is reached...
To Rickiev : I understand your point of view, but what I can not explain, it works fine for 45 minutes, then bufferings starts (also frequency of buffering increases). I have this issue only with some 4k VOD streaming (not all...), no issue with FHD or normal streaming.
Kind regards
Chocolate