I had to revisit retopology to fix some n-gons and tris. My multi-res data was saved externally. The new retopologized mesh is only slightly different from the previous with a few new loop cuts. After returning to multi res all the detail was lost. Attempts to pack the external file are not doing anything to the mesh(no I did not overwrite the external, I also have an external from a previous backup). What seems to be the problem?