Hi Kim. I'm having a very similar problem that began May 2. I have one podcast based on a URL (it's a paid subscription.) It has stopped updating with the below error message. I have tried deleting and re-adding but get an invalid feed address error. It works on other players and is a valid link.
https://www.stephaniemiller.com/feed/rss/
(this is not the full URL, I truncated my Member Key)
Here's the error:
SSLHandshakeException - Chain validation failed
-> CertificateException - Chain validation failed
-> CertPathValidatorException - Response is unreliable: its validity interval is out-of-date
-> CertPathValidatorException - Response is unreliable: its validity interval is out-of-date