This article describes how to fix an issue where the Virtual Controller reboots every hour.
This issue occurs if the IP address on the Virtual Controller changes, which causes the system ID to change. Because the system ID in the license file becomes outdated, the license becomes invalid.
To fix this issue, request a new license file on the Fortinet Support Portal and import it on the Wireless Controller. This will stabilise the Virtual Controller.
See the FortiWLC Deployment Guide for steps on how to import a license file.