For some reason I wasn't being notified of replies, I'll have to check my settings. Thanks all for your suggestions. I should have provided more details.
We don't have a storage device that supports NFS. I created an NFS share on a Windows server. It is mounted fine to our hosts in the production site. And the appvolumes data replicated to it from the production datastore.
We've worked with our firewall provider to ensure everything is open and we can see the traffic across the SD WAN but it just times out.
I am using NFS4.
In doing some random testing I had created the same type of share in the DR site and managed to connect 6 of 7 hosts to that share, one timed out. Additional testing, I removed the datastore from one host then it couldn't connect again.
Long story short it's probably something networking/firewall related but we're stumped.