Why do my meshes glow in the dark?

It’s a little difficult to make out but you can see a distinctive glow around the edge of each mesh.

None of their materials have emissive lighting or anything like that and there is currently nothing producing light on the level as the sun is down.

If anyone has any ideas what could be potentially causing this it would be greatly appreciated!

Do you have skylight in the scene somewhere?

Yes, but at “night” it’s intensity is also 0

This is a Dinamic Light issue.
Regardless of the skylight being set to 0, any intensity at all on the dynamic light during night time will cause some geometry that protrudes under the landscape to be lit.

A tried and true Fix All for this is to create a box as wide and long as the landscape and place it under it. I usually coat mine black and also disable shadow casting on it.
This perfectly prevents any light from ever getting to the foliage or any other mesh that was purposely sank into the landscape.

To work with large maps/worlds turning the light down to a really small number might be preferable to the box method.
This doesn’t always work, it depends on the post process and skylight settings as well.
Easy to tweak, hard to learn.

Well my ground isn’t a landscape it’s hism mesh tiles being instanced a whole bunch. And they aren’t lighting up? IT’s just my other meshes that sit on it.

No they sit on it, the mesh is about ‘100’ thick. And the sun is at the exact opposite side of the world at this point.

Do they sit on it, or do they poke through? It could still be related to the same dynamic light issue.

Experiment by turning off both skylight and directional light by 0. If they remain lit you at least eliminated the most common cause of this.

The next step would be to go through all the different buffers and see which one is still lit.