Edit: for https://www.circuitlab.com/ we saw all Stripe webhooks failing from 4:08am through 12:04pm PDT today with "TLS error". Since 12:04pm (5 minutes ago), some webhooks are succeeding and others are still failing.
Edit 2: since 12:17pm all webhooks are succeeding again. Thanks Stripe!
For backwards compatibility, I updated our intermediate certificates to provide the AAA Certificate Services signing https://censys.io/certificates/68b9c761219a5b1f0131784474665... to replace the expired 2nd intermediate certificate. (Modifying the "GandiStandardSSLCA2.pem" file in my case.)