Import Volumetric Lightmap Failed

Import Volumetric Lightmap Failed: Expected 520 tasks, only 497 were reported as completed from Swarm.

UE 4.27.2 (Mac) - Does anyone know what causes this? I have checked docs and it does not seem to mention any reasons for failing. Any help would be appreciated so I have some place to start resolving this. (Lighting builds fine, just the Import fails.)