Intermittently Backup & Replication application is unable to obtain an NFC ticket from vCenter Server, to go to ESXi and download a file from a datastore.
The delay is from a datastore.refresh operation introduced in a change in vpxd which introduced a call to datastore refresh each time a file Management ticket is requested.
Therefore, this is an issue with datastore.refresh taking too long which is a costly operation also exacerbated due to certain environments or certain datastores that are performing slowly.
The issue is resolved in vCenter Server 7.0 Update 3i (build 20845200).