What is more bizarre is that all of it's errors seem to be multiples of 60!
I'm wondering if it is confusing 60 based time (hour second) computations for regular multiplication?
Example:
xGPT 987 456 321
437 428919 199512 140397
654 645258 298224 209994
123 121401 56088 39483
x 987 456 321
437 431319 199272 140277
654 645498 298224 209934
123 121401 56088 39483
error 987 456 321
437 2400 -240 -120
654 240 0 -60
123 0 0 0