I am not certain but it seems that HW fingerprint of this device change in a way that ESMC requires manual approval for this device - it might have been evaluated as cloned.
Could you please check this client's details in console, whether there is no "Question" in respective subsection? It should be indicated by blue number. Also such questions from whole network should be listed in "Status overview" dashboard, if there are any.
If question will be reported for this device, please check documentation for it and resolve -> once done, device should be connecting.