@RachelTsegai26598 - are the MAC addresses still assigned to the expected Endpoint Identity Group (e.g. Registered Devices)? If not, then there might be a Purge configured to clear out endpoints.
But if it's just a case of them not being visible in the My Devices Portal then sounds like a TAC case to investigate why. It doesn't appear to be something that could be due to misconfiguration.