I was dealing with the same issue in TM 2019v1. The solution is doing the texture mapping in the modelling software you are using, in my case Vectorworks or SketchUp. Include the textures with your export to Twinmotion and then you can replace the correctly mapped textures with the high quality TM textures.
For some reason you can't rely on TM 2019v1 to do the texture mapping when the modelled object has no texture or only a color. This is a known problem with TM 2019v1 that didn't occur in TM 2018.
Hope this helps!