Myself and several of my friends are having this issue. I was on the final boss of vMSA last night and suddenly was taking nonexistent damage (not soul churn). I beat it every week for my weekly reward and ended up just turning my PlayStation off in frustration.
Bsses moving without a walk animation, sped up attacks, Voriak throwing skulls randomly (instead of typical timing) got stuck outside a portal, received a random speed boost and lost use of all my skills while killing the crystals...
Pretty much unplayable. I had issues in other rounds too but I just pushed through them.
Lots and lots of lag and delay.
Stormproof 1/7/16
V16 Magicka Templar
V16 DK Tank
V16 Stam Nightblade
V16 Sorcerer
V13 Stamplar
PS4 Player