Bug Unity 2020.1.8f1 generates incorrect maskmaps when upgrading materials?

I'm not sure what's causing this.
Mask map is generated from Standard (Specular Setup) material with: Albedo, Specular, Normal Map, Height Map, and Occlusion Map.

Result mask map becomes a 32x8 mask map texture, instead of being 2048x2048.

I've test it on this free asset:
https://assetstore.unity.com/packages/3d/vehicles/russian-military-vehicles-lite-t90-104569

Anyone has encountered same behaviour?