We involved USPS and our postage vendor Stamps in the investigation of this issue. The conclusion was that Stamps had experienced a system issue where they were recycling tracking numbers before the intended 120 day expiry of the old tracking data.
USPS cannot change the tracking history that is showing online to show the current delivery events. However items have still been delivered to customers successfully, and customers who don't have their item yet should have it by this weekend.
Affected orders usually had their label created/shipped date as 24th Nov. We have also seen a small handful of orders shipped in the days after the 24th that have November tracking history, but not for the package we sent. Checking the tracking history in these cases will show the package was sent from somewhere that wasn't Florida, where we ship from.
We are very sorry for the trouble this issue has caused our sellers, and if you have any specific situations you need assistance with, please reach out to our support team.