I experienced something similar with the fluxer-bin package in AUR. While trying to figure out if there was an issue open already I left the application open in that "view" and eventually I got the popup for using the passkey to login.
My guess would be that it's checking for the relevant endpoint with some timeout on the requests and retries, and eventually it times-out and shows the desired view. Could be completely off base tho, haven't had the time to look into the code.
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Comment by @GaidarOS