Apparently visionOS takes care of background tasks when its not in use, like syncing iCloud backups, getting notifications, etc. In some cases, users report the iCloud backup getting struck, causing lots of heat. The trouble is the front cover blocks the fan intakes and exhausts which apparently the vision pro needs in order to avoid the excess heat. And it's the stress from this heat that causes the front panel to crack.
According to Apple's support documentation, the AVP shuts off after 24 hours of non-use:
https://support.apple.com/en-us/117740
But it seems like that is not good enough. Better to unplug than risk damage to your AVP.
Hopefully Apple issues a software fix for this, like they did for the AirPods Max battery drain (again, because the 24-hour shut-off was too long)