That's weird, was that out of the blue or had you upgraded the drivers recently?
I have been having strange issues with boss fights since the night of the legion launch. I thought it was some of the addons I had recently installed, which was why I disabled lots of them.
I had to roll my driver back a few months ago, after updating it caused me massive frame rate loss in Ark. I don't think I have updated them since. Which may have been the issue, I'm hoping the new one, which is "optimised for Legion" is better. It's weird that I only had issues playing WoW and only in group content during boss fights. I played Armoured Warfare fine on Wednesday and solo quested fine in WoW since the expansion dropped. I'll have to see how things go tonight.
I'm hoping to get a new PC soon any way. My laptop is from 2014 and I don't think the 880M cuts it anymore. Also I'm not travelling for work all the time now, so switching back to a desktop would get me more for my money.