Yeah the more I think about it the more this makes sense to me.

Both were lighter than expected (so if it was a swap with another aircraft we wouldn't necessarily know - possible that 4 aircraft got the wrong data and we don't know the other two).

But it feels more likely that the sums just failed and they incorrectly caught the failures instead of letting it fall out. catch(e){} is a bug factory for sure.

That seems plausible. E.g., if the package cargo API timed out it could be treated as a 0.

That was my guess as I've seen people use non fatal timeout conditions and keep processing when a value isn't returned from an external data source.