VM retrieval fails during backup query

We have a number of VMware policies within our NBU 7.6.x environment which query vCenter for string matches in the annotation field.

A test query I ran today returned ~415 'includes' and about 1100 'excludes', which is  accurate.

But here's what's odd.  After the policy fires off, on an infrequent basis we'll encounter a VMware-side error that results in a subset of those 415 being selected for inclusion.  The error is as follows:

3/23/2016 20:19:05 - Warning nbpem (pid=11558) VM retrieval failed, server = [ASDFVCPTCCP01.domain.com]. 
Operation Status: 1

Anybody else seen this behavior?  It shows up about once a week, but unpredictably.

Thanks for any insight!