Problem I see is being in the meter socket, it would likely be easy to test at the service disconnect and be able to say it is upstream.
POCO pulls meter visual test looks good, they plug meter back in and possibly inspect connections in the transformer and then say it's not our problem. Yet they dropped the ball or at least needed to let the EC do some testing while meter pedestal is open, and likely need to allow some bypassing of the meter to be able to access that neutral terminal while testing it under load. Alligator clip pigtail with heat gun plugged in for a minute or two would likely been sufficient to find the problem they can afford the less than a cent of lost energy used during the test.