There are multiple reasons for Host-not ready status . If Vibs are not available,if there is a communication issue between Host-VC-VCNS etc .. Most of the cases VCNS,VC&ESXI host logs are helpful . You should certainly check that once also you could try below step
Try creating a test cluster and move the host(In your case host 2 & 6) to that cluster and move the host back to original cluster.
Cheers, Sree | VCIX-5X| VCAP-5X| VExpert 6x|Cisco Certified Specialist Please KUDO helpful posts and mark the thread as solved if answered