In Red Hat Satellite 6, manifest import or refresh fails with "Validation failed" error

Issue

• Importing or refreshing a manifest while some other random updates are done concurrently to the Red Hat Satellite.
• The import/refresh task fails with, Validation failed: Hostgroups expecting hostgroups used by hosts or inherited (check mismatches report)., Environments expecting environments used by hosts or inherited (check mismatches report). .. (or similar) warning.