Youtube freezing on Ubuntu 18.04

This happened to me too. It turns out to be a Chrome issue. Neither FF not Epiphany makes momentary sticky freezes nor halts while video playing. (decoding)

When you check chrome://gpu/ you will notice that Hardware Protected Video Decode part indicates that hardware acceleration is not available in Linux. Inorder to fix that go to chrome://flags/ and enable the Override software rendering list and restart Chrome. It worked for me.