Animation and Rigging Tools: FAQ, Known Issues and Feature Roadmap

Hey there! Sorry for the late reply again.

I have not tested the whole mixamo thing myself, but if it truly is the UE4 skeleton with a couple weird issues, you should be able to export the weights using ART, then use that skeleton as a snapping point for the joint movers, then the weights will get reimported.
Now your character will be fully ART converted.

“- If I zero-our everything ( except for the 90° ) I’m not able to build the rig since ART tells me that there are pre and post scripts in the scene, and the rig fails miserably”

This is interesting. In the publish screen, are there actually pre and post scripts listed in that section? If you clear them out, does it build then?