When a client operates at a high framerate on a dedicated server, their player movement will become desynced with the server. This manifests in different ways on different versions. In 4.21, it causes intermittent desyncs, causing the character to jitter and teleport around when the server corrects the movement. In 4.22 and onward (tested in Main CL#5915479) the player's movement will become completely desynced and no longer replicate.
This has been determined to be caused by background network packets saturating the connection so RPCs and properties can't replicate.
This occurs in 4.21
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-72965 in the post.