If you import an OBJ with new UVs then they will automatically update as long as the vertex order is the same between meshes. This makes copying and pasting UVs with UV Master a useless step, and one that could cause even more issues if the vertex order has changed. In this particular case, all your UVs have disconnected…
...which makes no sense in tangent space with both the normal and UVs smoothed. It worked properly for some time and just started going full retard on me. I've been laying out the UVs for this particular model after the fact through UV layout. Here's the particular workflow for it (worked twice and the third started…