Broken Movement or Collision near Parts - Engine Bug?

I’m unsure which category to put this in as I don’t know the issue here. It could be a code issue, but the nature of it makes me think otherwise.

My custom character has glitchy movement is a specific area of my game:

In studio I tried using Roblox’s Streaming debugger and nothing seemed to be wrong. The Focus of the camera is the HumanoidRootPart’s CFrame, so it doesn’t seem to be this issue. I also use RequestStreamAroundAsync, which seems also to be working.

This happens in studio and in-game. Any ideas on what it could be? Maybe someone else encountered an issue like this.

Do you have a Part or a MeshPart that it’s colliding with in that area?

Go to File > Settings > Physics, and check the Are Contact Points Shown tool.
This will show you a red sphere where there is contact between items when you test the game.

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Not that I can see. I highlighted the area and no parts or meshparts are covering that area. I turned on the Are Contact Points Shown tool, and here’s the result:

The player still seems to be correctly colliding with the Terrain despite the odd movement.

@Scottifly After looking into more physics effects, it looks like the border parts are causing the issue, though they never did this before:

In the video, I turned off CanCollide on the Part and that fixed the problem. That said, I need that part to have CanCollide on. How do I fix the wrong collision issue here?

There should be red spheres where your avatar is hitting the Terrain wall too.

What happens if you print out what the Position of the rig actually is versus what it’s supposed to be in your movement script to see what the numbers are while this is happening?

Does your movement script rely on Raycasts or shapecasts and there are issues with what those are hitting?

Where are your border parts located? Maybe try making them all Transparency .5 to show us exactly where they are.

Do your border Parts have any other Properties like CanQuery true?
Are they in a CollisionGroup?
Are they Unions? Concave Unions don’t always have the same physical shape as their visual shape.

I use a Humanoid and a standard StarterCharacter framework with a HumanoidRootPart (if that answers the question, not sure):
image

For movement, I don’t impact Roblox’s directional movement at all. Like the moving left and right and whatnot on the ground. I change behavior for jumping, but that doesn’t seem to be the issue. There are raycasts for moving platforms, but the script involved there isn’t the issue.


I think the collision by the engine isn’t being made correctly. There’s no way to change a part to Convex or StreamingMesh or whatever

CanQuery is True, I think. The property is hidden when the CanCollide property is True, which it is. There are no Unions in my game at all, and the parts here are not in a CollisionGroup.

Here’s a video of the properties:

Test with the hipheight really far up and see if the problem is still there.

yeah still broken:

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Do you have a custom movement system? Have you tried with a normal movement system? That looks weird.

If it is a custom movement system, does it work correctly with normal characters?

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After removing my custom Animate script (that controls my custom movement additions), the issue still happens:

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Ok I don’t know much about this so I might sound stupid, but can you rig a similar quick test StarterCharacter just out of parts and see if that has the issue too? It looks like it’s changing orientation based on what it’s over

Also try making it massless, see if that works, for what it’s worth.

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When removing the custom StarterCharacter (and using my Roblox character that Roblox forces) there still seems to be collisions (shown by the green flashing around the character), but the Roblox character doesn’t start going crazy like my character:

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If you can, see if there’s a problem when the startercharacter is massless, and if seperate, turn off cancollide for the feet.

If this doesn’t work, try making a test StarterCharacter similar to the normal one but just out of parts.

Sorry if this is a hassle, this is pretty unique and I haven’t seen it before, so figuring out what causes the issue is probably a priority here.

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Making the character massless did not fix the issue.

Making the character out of parts will take a bit of time, and I don’t think the outcome will change, but I’ll do it to rule it out.


To show that collision with Roblox’s Part is the issue, I made a new part in place of the old one and got rid of all the other parts. When I turn off CanCollide on that specific part, things go back to normal:

also no worries and thanks for replying


As a side note, turning off StreamingEnabled does not fix the issue.

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I meant to make some sort of four legged StarterCharacter out of parts and try it with that.

You may also be able to set cancollide off for the bottommost part of the startercharacter and make up for this with HipHeight, aslong as something else has CanCollide. You should try this with the feet/legs of your main startercharacter.

I’ve fixed the issue! It turns out that the Torso MeshPart in my StarterCharacter was missing a MeshId. When moving various things from one character to another, the MeshId must not have transferred over. Or, Roblox moderated the specific MeshId, I’m unsure.

There’s some odd behavior for the MeshPart too. Roblox thinks the mesh is bigger than it it. The Size of the MeshPart is one thing, being visually fine shown by when I make the Transparency = 0. However, when I press F to view the mesh with Roblox Studio’s Camera, the mesh appears to be really big. I think that was impacting the collisions:

When I switched that MeshPart Torso to a Part, my issue was fixed:


I found the core issue by making a Repro file with a new baseplate and just the starter character. I removed every part or piece one by one till I found the issue. From there, I messed with properties, saw the issue of no MeshId, and switched to a Part. After testing, my issue was fixed.

here’s the Repro file btw, idk if the thing of having no meshId causing collision issues is a bug, but it might be:
ReproToShowCollisionIssue.rbxl (243.8 KB)

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