Not a new bug but still exists. Quite often one will not gain any stacks when attacking with a primary skill with the Gears of Dreadlands set equipped. This can have other impacts as well where if using Focus and Restraint one will also not gain the resource-generating buff. This seems to happen most often while Strafing and in higher density areas.
There is also a problem where sometimes a primary skill will not attack if holding down Strafe and pressing the primary attack button.
Let me guess, Calamity…
https://us.forums.blizzard.com/en/d3/search?q=calamity%20momentum%20category%3A23%20order%3Alatest
It happens even without Calamity. I notice it most when strafing for a while without interrupting it to manually fire primary. At that point, the first couple or so primary firings don’t add stacks. You then have to fire several more before they register. As long as you don’t strafe for too long a duration before manually firing primary, it seems to solve this issue.