The certificate for domain 'imap-east.ge.xfinity.com' is untrusted.

All day (9/12/2022), the Comcast mail system has been error-prone. In most cases, it just times out and suggests trying later (not an option for me). Now it seems that a problem is with a certificate. 

The message is:  "The certificate for domain 'IMAP-east.ge.xfinity.com' is untrusted."  So, where do we go with this creaky system?  Tests run from an iPhone or an IPad do not reveal a problem, but the laptop browser version (Google, Firefox, Edge) definitely does have a problem.

What can I do to identify the problem, and what is Concast doing to fix the problem?

Bob