Character position replication Breaking with Motor6D/Welds & TweenService

Bug

If you weld (Motor6D or Weld) an object to a player and then use the TweenService on that object, the player will appear to run in place as their CFrame is not being replicated properly to other clients. This bug happens everytime you reproduce the scenario.

Reproduction

Clone or insert an object into the workspace and weld it to one of the player’s body parts using a Motor6D or a Weld. Proceed to change the size of the object with the TweenService. Look at the player with another client, and you will see that they are running in place until the Tweening stops.

Place: replicationBreakingRepro.rbxl (18.8 KB)

  • Use play test to spawn in two clients
  • Watch each client side by side and notice the failure to replicate movements

Where

This bug happens in real servers and test servers.

Example

https://gyazo.com/ed6bcf40d8a703467a8eed6b5bc5852b

When

I’m unsure of when exactly this started happening, but someone told me they’ve experienced it for quite a while (over a year).

1 Like

Just to confirm I reproduced same problem with your repro file.

1 Like

Same thing happens to me when using the tween service to size a welded object to my character. Localy it would look fine but for others you’d freeze in place just like that gif and teleport when the tweening is done to where ur client is