java "failed to validate certificate" but clears a while later?

Question

I've got an old java webstart app, and it appears one of the certs (possibly just an intermediate cert) it uses expired in December '23. That is understandable, but the odd thing is that the app will how the "failed to validate certificate" message for about an hour or so sometimes, but then go away and the app just works for users. If the certificate is expired, then I would expect this to be either working or failed not a sometimes working. Anyone have any ideas what could be causing this?

I know that I can disable the certificate validation, but would just like to understand the inconsistent behaviour.