Unknown Physics change negatively affecting BodyMovers/Constraints

[PorchThatHuantsMe (House_Owner)]

this just randomly happened to me ingame and I jumped then it broke my legs , I will start vibrating exactly like Arenoir said and be able to jump high but in this case it breaks my legs and is not intentional

[R_obotz]

happening in my hockey game, and it’s interfering with my league

[ScipioAfrikanos]

@Cfw_Sky thanks for that report, we validated that setting FFlagSimSolverOptimizeIslandizerManager2 to False has fixed at least some physics issues we’re seeing.

We just turned this flag off, please let us know if you’re still seeing physics issues in your games.

[yourcomputerhasdied (noob)]

They stopped happening for me, It was definitely the flag causing it

[Arch_Mage]

Disabling the flag seems to have fixed the issues.

[yoolurs]

the issues are still persisting for me. Could there be a delay on the release for me since I see others claiming its working for them.

[ScipioAfrikanos]

Sorry to hear that @yoolurs . Could you please give me instructions to reproduce the physics issues which are affecting you?

-ScipioAfrikanos

[yoolurs]

I’m unsure how to reproduce it or whats causing it. I just know that my game is basically unplayable. You can see for yourself Walk On Walls Obby - Roblox

@HiddenKaiser offered some potential insight here:

@HiddenKaiser

Hello,

The issue that they are describing is almost surely a result of the todays issues with Quaternion calculation. (based on the walking on walls). I just tested and the issue has still not been fixed in my game

I hope this helps diagnose the issue

[HiddenKaiser]

To build on this, @EgoMoose ’s getRotationBetween (basically Quaternion.FromToRotation) produces different results before and after the update (tested and confirmed). Almost all things that “walk on walls” use this function. I have deduced that the issue is with the cframe calculations based on other people’s reports.

@EgoMoose

local function getRotationBetween(u, v, axis)
    local dot, uxv = u:Dot(v), u:Cross(v)
    if (dot < -0.99999) then return CFrame.fromAxisAngle(axis, math.pi) end
    return CFrame.new(0, 0, 0, uxv.x, uxv.y, uxv.z, 1 + dot)
end

Blue arrow: Surface Normal
White: FromToRotation UpVector after update

[hello42]

Hi,

This flag does not appear to be the cause of our issue.

[yoolurs]

Thank you so much for this insight. Hopefully it helps the staff.

[ScipioAfrikanos]

Thanks Yoolurs. We flipped two more flags and your Walk On Walls game now appears to be fixed (neat game btw P

Please let me know if you guys are seeing any more physics related issues.

-ScipioAfrikanos

[hello42]

Hi,

What flags were flipped/deleted appear to have solved the issue. But being that this was a multi-faceted issue affecting multiple different kinds of experiences, I’m going to leave the thread as unsolved until tomorrow ~12pm PST in case any more bug reports come in on our end.

Thank you for your help.

[ScipioAfrikanos]

Great, glad to hear it hello42 Anyone else who is still having issues, please feel free to chime in.

-ScipioAfrikanos

[JamonCastillo (Jamon)]

Looks to be related! Roughly 4-5 hours ago users in our game “The Black Cat” began to experience severe screen shaking and movement distortion in a “swaying movement” like a rotation along the X-Axis, I’ve attached a video to demonstrate. This issue appeared out of the blue but appears to have a connection with sitting down but can also randomly trigger while moving around our map! I’m posting because this issue was persisting to multiple users at the time of writing.

[bear2126]

External Media

happening here for me, but this is using the new physics character controller:

[asimo3089]

It would appear this issue has returned, for Jailbreak. If it’s the same issue. Multiple reports of broken gravity, imaginary collisions, etc.

[APandaPoet (APanda)]

What platforms are the reports coming from? Can you also include Roblox app version? Thanks!

[asimo3089]

Hearing a lot from Mobile. Not sure if mobile exclusive. Some are saying rejoining the game fixed it. Don’t know if this means they joined a different server without this change or if the change was reverted by the time they rejoined.

One user reported this happening across many games and it possibly being related to Union/Mesh collisions. I’m making a new thread as it sounds like it may be unrelated to this BodyMover change. Sorry!

New thread for this issue: Mesh/Union (?) Collisions are breaking across multiple games
Edit: Resolved, the unrelated issue I made a thread for was related a collision group race condition.

[BritishTrainspotting (BritishTrainspotter)]

I am also experiencing this issue with my trains. They are violently ripping themselves free from the rails and beyond the rod constraint restrictions by multiple factors of distance. Roblox’s quality assurance for any kind of public update is disgustingly awful, and it is frustrating to continue having to deal with these issues for years on end.