could not establish trust relationship for the SSL/TLS secure channe

This warning started lately for any set or modification command. Tasks completed successfully.

Any idea, certificates are valid. can any one assist best way to troubleshoot it?

WARNING: The cmdlet extension agent with the index 0 has thrown an exception in OnComplete(). The exception is:
System.Net.WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS
secure channel. ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid
according to the validation procedure.