The "Unable to find template...." errors you're seeing could just be red herrings. We'll see that in working cores as it does happen time to time. What errors are you seeing in the Map drive logs on the devices while in WinPE? Despite nothing changing with the Ivanti configuration, other components involved can change and cause things to not work. I would verify that all preferred server credentials test correctly and haven't become corrupt for some reason. Also, you might check IIS logs on the core for any non-200 status codes when devices attempt to utilize ServerAuthentication.asmx to decrypt preferred server credentials.