Have the same issue, but only when XenTools where installed already on that machine. When installing the Xentools 9.1.5 on a clean and fresh machine, it says: "Virtualization state: I/O optimized; Management Agent not installed". No reboot loop. I think it's related to the Windows Version, Xentools 9.1.5 seems to be not compatible with Windows 10 20H2. Citrix Case is open and I'm waiting for a response. Keep you updated.