SOLUTION:
On a long shot I started opening every single skeletal mesh from the content browser and I found two that crashed… the ONLY thing special about these two is they were background LOD versions of skeletal meshes that had their LOD0 capped at 25%
deleting these meshes manually in windows explorer and recreating them in the content browser fixed the levels not opening issue. This worked for me after much trial and error troubleshooting.