Issues and physics-related flinging caused by recent Roblox update

As of 8/25, I’ve started getting reports of strange issues and random flinging after using abilities in my game.


Randomly being teleported to the void after changing equips

Randomly being flung an extreme distance after dodging using a BodyVelocity

Using skills underwater can randomly fling

Using skills that involve CFraming the character can fling them afterwards

These are a few of the many examples of reports I’ve gotten since 8/25. Note, I have not updated my game in a few weeks, so these issues were not caused by something I did. I was hoping whatever physics-related change was pushed on 8/25 could be reverted, or, if this is a result of something else, tell me what I can do to fix it

(Also apologies for waiting so long to report this, I was moving on the day I was first informed of the bug)


I’ve disabled a recent bug fix that may have been responsible for this behavior change. Can you see if the problem still persists? Thanks.

Its still occurring in new servers


Is there any update on this? We’re still getting spammed with reports about flinging and I honestly have no idea what to do. I’ve looked over the code in the skills that are involved in reports the most but nothing seems out of place.

It seems like some kind of replication desync that only triggers via bodymovers from what I’ve seen. The skill that is causing most of the flings doesn’t even apply bodymovers to other players though, and yet I’ve gotten reports of players flinging even when far away from where the skill was used. All that skill does in particular is CFrame the user’s HumanoidRootPart around the center of where the skill was used randomly

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It probably has something to do with the fact that BodyMovers have a different stepping rate than other physics objects. (240hz)

Do you have PhysicsSteppingMethod set to Adaptive? There’s been reports of it making BodyMovers unstable, and you could potentially temporarily change it to Fixed to see if it makes a difference.


I already have it set to Fixed since Adaptive made players clip into the ground rarely for some reason


Since you mentioned that you’ve already set the PhysicsSteppingMethod to “fixed”, the problem likely resides elsewhere. As you stated before, one common issue with physics-based behaviors is related to synchronization between the client and server, especially in multiplayer settings. In the meantime, you could:

  • Implement additional server-side checks to validate that the physics-based actions being performed on the client-side are feasible before they’re executed. Essentially, before a player can use an ability that adjusts the CFrame, have the server validate that the move is acceptable. This won’t necessarily prevent a desync, but it can limit the impact of one by preventing invalid actions.
  • If the server disagrees with the client, you can then reset the client state to match the server, reducing the likelihood of players being flung or teleported.

This is a quick fix and not a definitive solution. If the problem truly lies in the recent Roblox engine changes, it might be more complicated to resolve entirely. You might still need to do a deeper dive to find out how the engine changes affect your specific use-cases, but the server validation step can act as a “sanity check” to mitigate the most disruptive symptoms.

Additionally, I’d recommend checking out the following post, if the issue you’re facing appears similar. Keep in mind that the BodyMover class is deprecated, so other methods are generally recommended.

We are experiencing flinging with our game’s large moving contraptions. Quite randomly they will get a massive velocity and just vanish into the void/nan space. This persists in the server until an admin gets called and we have to shut it down. I am curious if there is any A/B testing being done because 90% of servers are fine but certain servers are ‘bugged’ and cause physics flinging issues that persist until shutdown.


I’m unaware of any recent changes to BodyVelocity specifically but there could be changes to other parts of the physics system or networking that caused the change. Are you able to provide a simple reproduction of the problem? That would help us get to the bottom of things. Thanks.


After some more testing, it seems to only happen in-game, in servers with more than 1 player. I can’t get it to happen in play solo or in a studio test session with 2 players no matter how many times I try, but testing in game with someone else we got it to happen after a few tries.

I’ll try to make a repro file now

I wasn’t able to make a fully accurate repro, even in-game on the repro place we can’t get the fling to occur. My only idea now is that its some kind of network or physics replication issue, because we’ve also been getting reports of players’ ships randomly teleporting to the void as well. (Ships are an unanchored weldconstrainted model network owned by their owner player, with bodymovers to keep them in place)

This was the repro file I tried to make:
weird fling physics desync repro.rbxl (283.6 KB) (Press Q to use the “skill”)

Nothing happens in studio, and in-game the most we were able to get happen is slight flinging shown visually on other players right when the skill ends, which also happens in my game. (Not sure if that means anything, but that slight flinging did not happen until this bug started existing, so maybe its something?)

Also another note: The “slight flinging” only started occuring in the repro after I added the forced R15 2.0 body when you spawn in, so maybe the bug has something to do with ReplaceBodyPartR15 or BuildRigFromAttachments

If you want I can private message a copy of my game but I don’t know if it’d help. I’m probably going to try recoding the broken skill to use forces rather than CFraming the character to see if that helps, but then there’s still the issue of player ships randomly voiding


I had this happen again to one of our servers today. The physics contraptions assume a massive velocity (ie 251225125,-1251251251,125125152) and despawn. This persists across that entire server until it’s reset. It happens to maybe 1/100 servers randomly but makes for an incredibly frustrating experience as people report it as an ‘exploiter’ and we have to go and manually reset that server. It would be nice if we had access to more information about each server instance, and additionally a way to log physics interactions so I could know what interaction cause the object to assume such a large force

Thanks for posting the repro. When I open up the placefile and hit Q, the avatar will start acting funky. Is this intended behavior? Trying to clarify the part where you mentioned that ‘the problem only happens during live games’.

The skill is intended to CFrame the player’s character randomly around the point where they used it, dealing damage. In live servers, its only after the skill is over (after all forces are deleted) when flinging/voiding can occur

Thanks for the reply. So the random movements that I’m seeing is intended behavior correct? Then for the repro this is what I should expect:

  • Joint live game
  • Conjure skill, character will do random movements
  • After it finishes, it will fling

Can you confirm if this is what I should expect for the repro?

In live servers in the repro place, players don’t fling like how they do in my game after using the skill near each other, the most we were able to get happen is some weird desync visually on other player’s characters. You’ll notice that when a different player finishes using the skill in the repro, their character can “fling” a bit visually, but its only visible on your screen, the player doesn’t see their own character flinging afterwards. I’m not sure if this is the same type of issue that is causing the huge flinging/voiding in my game’s actual live servers.

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