merge material does not work if materials are using vertexInterpolator nodes

in 4.17.2
repro : have a static mesh with multiple materials some or all of them using a material that uses the vertexInterpolator node.
Use merge materials on this static mesh
->the merged material is not working.

Our lead programmer found a fix (some needed code wasn’t implemented for the case of vertex interpolator)
After his fix we were able to bake materials using vertexInterpolator.