Released: July 2021 Exchange Server Security Updates

Nino_Bilic Yes I know it wasn't expired.  
I also deployed a new OAuth certificate. As mentioned above.

And if it was expired the problem should exist before the update and wouldn't be fixed by uninstalling the update; the update does not change the certificates.

The one strange thing I had after installing the update that the script Get-ExchangeCertificate (Get-AuthConfig).CurrentCertificateThumbprint gives an error result with a thumbprint of a certificate which did not exist (and never has) on the server.  This thumbprint problem was solved after deploying a new OAuth certificate. But the ASSERT: HMACProvider.GetCertificates:protectionCertificates.Length<1 was still there.