Just to do this quickly I exported out your mesh as an OBJ from Houdini, and you have some UV issues. The reason why it wont load into Painter is due to some faces which are spanning outside of your tiles (one was really out there in negative space). Aside from that you do have a lot of overlapping in your UV map, so I wasn't sure if you have MAT IDs set up or something to separate those into their own sets.

Once you fix the outside parts it will work fine.

This is one of the reasons I wanted to see the mesh because I've looked at thousands of mesh files where people assumed their UVs are done properly and they had such issues.

You can see this in Houdini if you select to view your POINTS. They're at the bottom:
