Comodo code signing certificate is failing today

I have a code-signing certificate from Comodo (licensed to JP Software), valid until September 6, 2018.

This afternoon (somewhere between 2pm and 3pm EST) the certificate validation started failing, returning a CERT_E_EXPIRED error from the Windows WinVerifyTrust API. Shortly thereafter, I got several thousand irate emails & calls from my customers, whose app would no longer work.

Any idea why this certificate suddenly became non-functional? And any hope of getting a fixed certificate?