There is a periodic hitch that happens once every second on the 2018 open beta. This hitch happens in all worlds, but gets worse if you are in a world with many objects or have many avatars loaded. The hitch is quite noticeable in worlds with more than a few hundred objects in the scene.

I took some graphs of frame time using Intel GPA. The world I tested in just has a few lightmapped meshes: wrld_83a2a007-0d76-45e2-9607-fb97320933d6 this can be repro'd in all worlds I have visited and happens regardless of the avatar I am in as well. Re-uploading the world on 2018.4.9 does not seem to change the hitching.

The first attached screenshot is on live and the second is on the 2018 beta.