Looking at the IPs for the NFS share and for the hosts in the export policy, I see they are on different subnets.
This means that if you have multiple NICs in your CentOS and ubuntu systems, it will use whichever NIC holds the default route to mount the storage, this might be a different one to the one you plan. Can you confirm if there are multiple NICs in these VMs and if so, what the IPs are?