RHEL VMs lose connection to Isilon NFS mounts randomly

Has anyone experienced hosts randomly losing connectivity to the isilon?  here is a scrubbed output from the server that lost it's mount.  you will see that a df-hT shows it lost connectivity.  I verified the settings are correct in /etc/fstab.  I unmounted and mounted and it came back lickity-split.  I have around 200 connected clients and it randomly occurs.  Any assistance would be appreciated.  I've also opened a case, so if know one knows I'll post the resolution once found.  thanks in advance

[user@rhel-host ~]$ df -hT

Filesystem    Type Size  Used Avail Use% Mounted on

df: `/apps/rhelFS/nfs': Input/output error

[user@rhel-host ~]$ more /etc/fstab

isilon-nfs01:/ifs/data/nfs/customer/rhelFS-nfs01 /apps/rhelFS/nfs      nfs rw,vers=3,hard,bg,nolock,dirsync,acdirmax=1,acdirmin=1,lookupcache=none 0 0

[user@rhel-host ~]$ sudo su

[root@rhel-host user1]# umount /apps/rhelFS/nfs

[root@rhel-host user1]# mount -a

[root@rhel-host user1]# df -hT

Filesystem    Type Size  Used Avail Use% Mounted on

isilon-nfs01:/ifs/data/nfs/customer/rhelFS-nfs01

nfs     95T  9.8T   83T  11% /apps/rhelFS/nfs