I am in Europe on a 50/5 Mbit line and youtube is just slow and always buffers if i try to watch something HD in the evening. Speedtests give me 40-50Mbit const

I am in Europe on a 50/5 Mbit line and youtube is just slow and always buffers if i try to watch something HD in the evening. Speedtests give me 40-50Mbit constantly so it has to be a Youtube issue... very annoying :/