BGW320-500 interfering with UDP/443 traffic in the last 7-10 days, for multiple users across the US

Among thousands of users we now have a growing number spread across the states that can not use QUIC applications (in this specific case, SMB over QUIC) UDP/443, and the only they ALL have in common is ATT service, specifically using the BGW320-500 modem. Must be some recent firmware update that needs a fix? I'll try to gather specific version info, but we aren't allowed to "touch" customer owned equipment so, it may be tricky. Is there a good contact at ATT to reach out to? I haven't had luck with their support or NOC. We're advising all affected users to push for replacement modems of a different model.