Odd movement bug - movement slows until I move left or right

[InsaneRAE]

So for the last two days or so I've had this bug. While walking forward, backward, or spinning left/right, my movement slows to a crawl. It takes a second to happen after starting running. Animation wise it's like the animation cycle is stuck in the center of the walk (moving back foot to under the torso then jittering back and forth slightly). Speed-wise it's about the speed of moving while ducking.

EDIT: Apparently it has something to do with my keyboard. Used my wireless one and I don't have this problem. My normal keyboard has plenty of options but I'd already reset to factory defaults.

If I use the right click + left click method or auto-run this doesn't occur.

Once I hit left or right, the jittering stops. But starts again as soon as I let go and press again the forward/backward key.

This is on my halfling. Has occurred over multiple sessions, in multiple zones. Made a human, same thing happens.

Here's a gif I made: https://imgur.com/g5wuat7

I start by walking forward and slowness starts. Then I demonstrate the same slowness trying to rotate left/right.

Any ideas?