I have recently noticed in 2 of my FBA shipments, Amazon received approx 120 units (60 in each) extra units than what I sent.

While I'm not complaining about getting free stock, I obviously don't want this to be at the expense of another seller, which I feel it likely is. I also don't want this to cause any problems in the future.

Has anyone else experienced this? Can anyone recommend the best course of action for this?

Thanks.