I have this also. If you use the console command ‘stat graph’, you see this jagged trend
You’ll notice the jogging effect is in time with the green spike. For me, it’s about 2 - 3 times per second. It might be related to the Zen loader.
I think it might also be somehow related to something weird going on with the wrong textures mips getting streamed
A fix isn’t on the cards until 5.5 
PS: I think you’ll find this doesn’t happen in a standalone game?