After reading your question, I found that I had more questions than answers. For example, what version of NFS are you using (NFSv4 is not supported)? However, after taking a few minutes to think about this, it's better handled in a SR. I suspect we will need to look at the NFS and figure out what's going wrong there. It could be anything from firewalls to network saturation. Then we will likely need to check the validity of your metadata, and potentially clean up issues. It won't probably be simple or easy, and we don't want your data here.
Thanks for the reply. I have logged an SR so we'll see what happens.