This should probably be in engine bugs, but I am pretty sure you need to be a regular. I am mostly certain that this is an engine bug, I don’t know how you can fix it, but you could make the doubled sided property in roblox studio to true on the mesh, see if that fixes it.
This has also happened to me, what I did was just fill the space with a block in the game or double patch it in that spot. Hope this helps and it should work.
It looks like you need to triangulate your mesh and export it again. It’s hard to tell though and if this doesn’t work please provide a picture of the asset’s wireframe in Blender.