90% of the time this is 1 of 2 things:
  1. Performance lag on the PC overall causing some variation in movement.
  2. Input lag caused by your software or hardware KM

The former can usually be attenuated by adjusting settings lower or capping framerates.

The second can be a real problem. Obvious things to check here are that your WoWs are all set to low process priority and your software KM is set to high priority. Hardware (wireless) setups can suffer from latency and missed keystrokes if they're low on battery or one or more receivers are too far from the device.

Lots of things to check. I'd start by limiting framerates (MAXFPS) on all clients and turning down details and see if that helps. If it does help immediately, then you're just overtaxing your system and it's an easy fix.