Because you still need to have a valid pro license? the e5 subscription activation gives you an UPGRADE to enterprise... and with an upgrade you need to have the pro in place. So first I would start making sure if the device was already activated with a valid pro license. Using KMS or ?
I thought that once you move your license to Microsoft 365 E5 you do not need KMS. We have shutdown our KMS server and once you add the device to Intune, should it not get the Microsoft 365 E5 license (If it has been assigned to all the users).
I am not an expert in licensing but my desktop folks say that yes it was activated with a Pro license and it comes from the OEM.