First of all, sorry for the inconvenience. As you said, during the redesign of Thor pieces in Freecad 0.19 I missed that cutout of the Art1Body part.
I just have updated the Thor GitHub repository with the fixed FreeCAD, stl and step files corresponding to Art1Body part. If you have not printed the v1.0 version yet, it would be nice to print the new one instead of the v1.0 version.
Thanks a lot for the report! 🙂