I will take a wild guess (based on that you are using firefox) is that you probably have enabled the various don't save cookies, clear sessions on close or other hardened privacy settings that are the source of 99% of problems firefox users encounter, like increased cloudflare captchas .

Could be! I don't recall turning things like those on, I use firefox for features not privacy, and mostly leave stuff like that at their defaults, which I trust Mozilla + uBlock to filter the invasive trackers while leaving actually useful functionality, but it's possible I fiddled with it years ago and forgot.

Some probably kinda strong counterevidence to that though is that this doesn't happen on all sites, only Amazon. I've never been prompted to make a new passkey after passkey login on the 12 other sites that I have passkeys in bitwarden for.