Invisible barriers on side of simple unions?

Hey, I am working with unions to create doors but there is some weird barrier in game whenever I do it. It is weird because no matter how long the opening is, the barrier is always on the sides. I have no idea what to do as I tried deleting models around them and full on redoing the unions. It is happening in multiple unrelated locations.
pic 1
pic 2
In the second image, you can see I moved away the door and even deleted it at some point so it can’t be that affecting it.
This is super frustrating as I am almost done with the game so any help is appreciated! Thank you

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Removing small percentages of Unions (like a small door in a large Part or Union doesn’t give an exact collision opening.
Unions and MeshParts have a separate physical collision box compared to the visual representation.
Try the Search bar up top, there are dozens of previous posts about this exact same issue.

I used the search bar but only found people saying to change the RenderFidelity to Precise and change the CollisionFidelity to PreciseConvexDecomposition. This worked for one of them but made all of the others worse, as now I can’t even walk through the opening.

Would it be better to not use unions and just use three parts? I’m worried that it would look messy but at this point I may just use that since unions didn’t work the way I thought.

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Don’t use unions for walls when you can avoid it. Anything that a player needs to move through or interact with directly should generally be made from parts. Unions are better saved for detailing specific sections or creating shapes not otherwise possible.

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I used to have this issue sometimes. If it is something simple, I would just use parts.

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Yes, instead of a Union just use 3 Parts.
If you are using a Material with no real pattern to it like Plastic or SmoothPlastic you’ll hardly see the difference. If you are going to use Wood or Granite for example, the Part edges will be more visible.

You can also check your Union’s actual shape using the ShowDecompositionGeometry tool in your PhysicsSettings. There is also a Plugin that does this for MeshParts and Unions: CloneTrooper1019’s Mesh Optimization Tools - Roblox which is way easier than changing your Physics settings.

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