Intune - Several Mobile Devices have the status "Blocked"?

If you face any issue with Intune-ConfMgr managed mobile devices, where some devices appear as "blocked" in the confMgr console, then you need to check the following:

Can you confirm if any of these users were ever removed from the Intune User collection, under Configuration Manager console, after enrollment?

If so, that would block the devices as the user would no longer be licensed, breaking the link between device and user, thus blocking the device..