Twitch.tv causes system to hang and requires reboot

I was initially having issues with youtube causing a system hang and needing a reboot but fixed this by disabling hardware acceleration.

But loading a twitch stream instantly causes the system to hang although the audio plays and requires a reboot.

About this mac: iMac (Retina 5K, 27-inch, Mid 2015) Processor 3.29 GHz Intel Core i5 Memory 16 GB 1777 MHz DDR3 Graphics AMD Radeon R9 380X 4096 MB