RHEV - install of VMs issues

Hi,

For a very long time (started with rhev 3.0 and still exists in rhev 3.2) we have had issues when installing a VM.
The issue seemed to be the NFS-share from which the iso we start the installation.

The problem:
I attach a bootable ISO which is 40MB.
I start the VM in "run once" with the ISO attached.

The VM goes to "starting up", nothing happens, and then to "Not responding".
If I log into the host and try listing the files in NFS share (or running df) it hangs/freezes.
Going back to the GUI I can see the ISO storage has changed to "inactive".
In this state it sits for a very long time.

What makes matter worse:
Sometimes it works.
It's not related to a single host or a single network.
The NFS share works if I try accessing it from a server (in the same network as the NFS-server).
IT could be network-related.
We have following ports open between hosts and NFS-server:
TCP and UDP: 2049, 111, 892 and 662.
TCP only: 32803
UDP only: 32769

Anyone have the same/similiar issue? Any advise on debugging this?