I am cloning a Windows Server 2012 R2 template using a customisation spec. All pretty standard. It joins a domain, and I assign an IP address manually at clone time
usually the clone and sysprep takes about 8 minutes, however just recently about 1 in 3 clones take about half an hour. Looking at the events in Vcenter sysprep starts and finished successfully. This corresponds with a drop in the CPU, but then it just sits there doing nothing. During this time however I can see it hasn't joined the domain as there is no computer object in the domain.
Looking at the log files of these machines it just seems to stop, and I can see the Sysprep_Succeeded.tag file in c:\windows\system32\sysprep.
Any ideas why this might be? As far as I am aware no changes have occurred on Vcenter. We are running vcenter 5.5 and ESXi 5.1.