Custom image stitched from vanilla assets fails to upload/update

Description:

Dear Age of Empires II: Definitive Edition support team,

I am encountering an issue while trying to update my local mod to the mod workshop. The mod works perfectly when installed locally, but I cannot successfully upload the new version.

What I did:

I created a new graphic by stitching together multiple official in-game images (all assets are from the base game, no external imports).

The mod loads and displays correctly when I enable it in-game.

When I try to update the mod (either through the in-game mod manager or via the website Mods All - Age of Empires - World's Edge Studio ), the process fails.

Could you please advise if there is any known limitation or a workaround? I can provide the mod folder or the file if needed.

Thank you for your help.