It's made the news yesterday, but in case you missed it, there seems to be a bug within vSphere 5.5U1 that affects all NFS users.
NetApp & VMware (at least, maybe Nutanix too?) are working on the subject.
See the post below for more information:
That may also explain the delay from Nutanix in the support of the 5.5U1?
Did you guys catch this while working no the 5.5U1 support?