It may be due to the "coating", which ensures child safety. You can read about it in various forums.

Just in case someone is also considering buying these batteries: there could be problems with this product.

I have this issue with multiple brands, there are different problems in the AirTag use case, one of them is, the AirTags itself. They simply don’t work perfectly. I have switched batteries from AirTag to AirTag and sometimes AirTags report same battery to be okay and to be low battery.
Then, there is the battery itself, it’s voltage as MINT condition and its capacity.

I have seen batteries that comes as new with barely 3.1v while other brands comes with 3.4v

Over that there are battery contact issues. Tolerances of battery dimensions poorly taken in consideration by Apple. On top of that, there is these famous bitter coating so babies don’t swallow these batteries (which not all brands have)

Conclision, get the ikea cr2032 for AirTags, cheap and decent battery capacity.

Varta and Duracell CR2032 batteries have 230 mAh. The GP batteries only have 220 mAh, maybe that's the reason?