material morph issue

Hello,
We are having difficulties with appending a scene with placeholder materials, then replacing the placeholder materials with textured materials from the main scene. The model(a gate) morphs vertically and horizontally, the frame is a separate element, and each plank is taken separately. Planks do get the proper material change and work without problems, the frame(multimaterial) turns black as if there were no texture.
In order to do the switch I modified the assignMat function from Verge to pick the right material from the object to switch:
var firstSubmesh = obj.resolveMultiMaterial()[pos]; <-pos is the proper material slot that I calculate.

Also, I noticed for the gate frame itself that without cloning the material, morphing sometimes does not work as intended.

Any ways we can circumvent these issues?

Dragos