Updated to add
The Register understands from sources familiar with the matter that HP Inc asked Apple to revoke its printer driver code-signing certificates. It appears this request backfired as it left users unable to print. A HP Inc spokesperson told us on Friday night:

We unintentionally revoked credentials on some older versions of Mac drivers. This caused a temporary disruption for those customers and we are working with Apple to restore the drivers. In the meantime, we recommend users experiencing this problem to uninstall the HP driver and use the native AirPrint driver to print to …