Never had this problem with other classes, until I started playing Primalist. Was not sure at first, but it seems that swipe is the skill to blame. Totem Shaman didn’t have this problem, but melee Primalists did.
What happens is that my usual routine is to press LMB to run to next pack of mobs, then spam/hold RMB to use Swipe. And occasionally after using Swipe, LMB stops working. The character stays in place, until I use a skill other than movement. Like swing a Swipe one more time, or Leap.