Azure VM reboots exactly 1 hour after startup

Question

Problem:
All VMs created from our custom images (VHD files from a Storage Account), all reboot exactly 1 hour after first starting up in Azure.

Symptoms:

• After the 1-hour reboot, the VM will remain UP consistently from that point.
• However, if you stop and de-allocate the VM, then start it... it will reboot again after 1 hour.
• The only hint of evidence from within the VM, is a shutdown event from svchost.exe, without any details or nearby events that help narrow the root cause.

Steps to reproduce:
1- In local Hyper-V, create and setup a Win10 VM. Optionally customize the wallpaper as you see fit. Don't sysprep.

2- Shutdown the local VM, and using 'Edit Disk', convert it to a fixed-size VHD format.

3- Upload the VHD to your Azure Storage Account.

4- Register an image, pointing to the VHD uploaded in the storage blob.

5- Deploy a VM from that image. After 1 hour from startup, it will unexpectedly reboot.