Это раньше случалось, но обычно при установке CU - In some cases, certificate is not assigned to Exchange Backend site (probably causes by previous CU installations), but everything works fine for customers. Although according to the article below OWA, EAS and etc. should not work anymore.
https://support.microsoft.com/ru-ru/kb/2779694This behavior probably caused by permanent IIS cache of SSL cert bindings (isn’t clear after server is rebooted).
You can review cache entries like that:
netsh http show sslcert The issue is, that actually binding still persists, but pointing to non-existing certificate. In our case we have self-signed certificate in personal certs store, but thumbprint is not the same as listed in bindings.
Looks like IIS manager is smart and trying to find “Display Name” of certificate, not able to do it and show binding as unassigned.