Discrepancy in Lightsail Data Transfer Out Charges Despite Below-Allowance Usage

Hello AWS Community,

I've encountered an issue with my AWS Lightsail billing, specifically relating to data transfer out charges, and I'm seeking guidance to understand the discrepancy better. My Lightsail plan includes a 3TB data transfer allowance, and upon reviewing my usage across all instances, I've confirmed that none individually or collectively exceeded this limit. Despite this, my bill reflects a charge for exceeding the data transfer allowance, with a noted overage of 402.717 GB, leading to a charge of USD 36.24 at a rate of $0.09/GB.

To investigate, I used the following AWS CLI command for each instance to assess the "NetworkOut" metric over the concerned billing period:

aws lightsail get-instance-metric-data \
    --instance-name "InstanceName" \
    --metric-name "NetworkOut" \
    --period 86400 \
    --start-time "2024-03-01T00:00:00Z" \
    --end-time "2024-03-26T23:59:59Z" \
    --unit "Bytes" \
    --statistics "Sum"

Despite this, the aggregated outbound traffic does not seem to align with the overage charge. I ensured that all instances and relevant services within the Lightsail account were accounted for during this period.

Questions:

1 - Are there any known issues or nuances with how Lightsail calculates data transfer out that might lead to apparent discrepancies in billing? 2 - Is there a more detailed method or another approach I should take to accurately track or audit my data transfer usage against the billed amount? 3 - Would AWS Support directly provide usage records or logs that could clarify this discrepancy?

Any insights or guidance on how to proceed with resolving this discrepancy would be greatly appreciated. Thank you in advance for your assistance.