You could be able to try removing the contours by copying the mat_config file to the respective folder in your mod's folder and forcing the game to load them via the add.xml. But don't forget to remove the "CONTOUR" tag from the mat_config.

Wait what "CONTOUR" tag? Did they add a "contour.material_config" file for the loot? Because I'm not seeing them in my game file extract.

in the material_config for the loot asset, look at the render_template.
there's something that say contour or some word, that tells the game to gave contour to them

note that I've never deal with asset that have this, but thats usually how contour is done

Hmm...weird. The file for bnk_prop_vault_loot_value_d (The one causing the most problems) looks like this...

<materials version="3">
<material name="mat_jewels" render_template="generic:DIFFUSE_TEXTURE:NORMALMAP" version="2">
<diffuse_texture file="units/payday2/props/bnk_prop_vault_loot/bnk_prop_vault_loot_value_d_df"/>
<bump_normal_texture file="units/payday2/props/bnk_prop_vault_loot/bnk_prop_vault_loot_value_d_nm"/>
</material>
</materials>

However, I'm concerned my files are from an old version and aren't up to date, and I may need confirmation on this