Just started happening about 20 minutes ago. I had this problem before with a Razer Naga, and it's the same exact thing with my Feenix Nascita 2014. (note: i've had the nascita for months now)
It just randomly gets caught up on something...everything is clean and fine, it just randomly started doing it. It's very hard for me to describe, so I recorded myself attempting to do the best circles I can, but you can clearly see it spazzing out.
https://www.youtube.com/watch?v=1vCNON6x48M
Some parts you won't really notice, but it feels like it's being pulled the other way.