Welshwoman Eccles appeared bewildered when it was announced she had lost 3-2 on points.
The 28-year-old narrowly won the first round, was edged out in the second, and then lost the final round despite her opponent being docked a point for failing to keep her head up.
Only one of the five judges had Rygielska ahead on the scores – two had Eccles in front, while two scored it even.
However, in those circumstances, judges who give level scores then vote for who they think won, and both decided in favour of the Pole.
BBC boxing commentator Steve Bunce, who called the bout live, said he was “shocked and stunned”.
“That was a brutal outcome. I really did think she’d [Rosie Eccles] get it,” he said.
“We’ve got independent judges here. They went with the one who got deducted a point and she actually fouled.
“The two judges who had it even voted for the woman who had an infringement. I’m really annoyed. It’s a bad decision.”