Just wondering, did the original poster purchase their AirTags from a third-party reseller? If they got those first-generation ones from a third party and they were sitting in the warehouse for a while, this could be the reason, even if they still can’t work after putting the battery in and out.
To be honest, I got my second-generation AirTag directly from the Apple Store, so it won’t be an issue for me especially since that’s new stock. I did exchange it a bit before the return window closed because I initially used it for a school project. However, reverse engineering it in CAD caused it to get scratched easily by my callipers and measuring tape, and I removed the battery in and out a couple of times. After I finished my project, I got it exchanged at the Apple Store so I could have a fresh one with the battery still intact to use for my bag.