Is this because the certs were revoked? (Revocation is broken ;P)

Caddy staples Valid OCSP responses to all certificates that have an OCSP responder, so if browsers aren't accepting that, then arguably the clients are broken, because that response is valid until a few days from now. But before the 100% valid and trusted OCSP staple expires, Caddy will get a new staple that presumably says Revoked, and replace them right away before browsers would ever see a Revoked status.

(Revocation is broken ;P)