Material with more than 3 layers does not appear in the game.

[Rev0verDrive]

Once you hit the 16 unique textures you’ll want to start packing… texture channel packing. You should be doing this anyway if you’re thinking about publishing.

Here’s a decent thread on Texture Channel Packing.

Texture Packing for UE5 - Feedback Welcome

Nanite and Lumen slightly alter the focus of how textures are handled in UE5 (for example legacy AO is set to be superseded by Lumen), so I wanted to revisit the texture packing method I’ve been using on my projects up until now because the more I read, the more I realised how un-optimised and redundant it was. Even with the advances in poly count for meshes in Lumen and the help provided by virtual texturing, there’s still no getting around the limits of the good ol’ texture pool. I’m by no mea…

There’s also Texture Atlas.

How To Create a Texture Atlas Master Material in Unreal Engine 5 | Community...

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For your particular issue we’ll need to see your material setup.