What other integrations would this vcenter have, vsphere replication? You may want to open a support ticket, they can look through the vcenter logs to see what its trying to do, and those logs may have information you don't want to share here.
I think the hostd log tracks this, so you want to get the log from one of the hosts if your want to try and find it your self
VMware vSphere 5.1 (these are the same locations in general)
You may have redirected them to a datastore or somwhere else, if so you can look there directly.