Completely random. Sometimes I will log in and not experience anything for an hour or two then moving to a new town I will see them. Sometimes a player logging in will cause it and it will be attached to them.
WORKAROUND: To workaround this I can sometimes purge them by looking at the ground and turning vsync on and off. Vsync's status is not relevant as the issues persist with it on and off but cycling it seems to reload the scene and it will sometimes load without errors. I can sometimes play for a few hours and never experience the errors, other times I can not get rid of them and I have to stop playing.
NOTE: This has been an issue since launch and has persisted across re-installs, gxd river updates, game updates, ect.