From the article:

Both the “idle time”, which indicates a period of scanner downtime of ten minutes or more, and the “latency under ten minutes”, which tracks scanner interruptions between one and ten minutes are deemed illegal by the CNIL when it comes to data processing. The CNIL is using the GDPR as the legal basis of the case.

Amazon has also implemented a “stow machine gun” indicator to prevent mistakes. It signals an error if you scan an item less than 1.25 seconds after scanning the previous item. It sounds like a way to prevent double-scanning mistakes. But that’s a GDPR issue too, according to the CNIL.

I think these all seem like entirely reasonable things for Amazon to track.