When you say "nothing happens": what's the QR scanner? Do you have Chrome installed on the device? What are the app versions (from Settings) of Play Services and Chrome?
In my experience as the phone gets older features start to "deteriorate". For example, the previous phone didn't make or receive telephone calls after a few weeks without rebooting, this Pixel 2 ceases to work as a Contactless payment device after a few days without rebooting, and FIDO is the same way, so, maybe try rebooting? I figure that one day Google will rewrite their core systems in Rust or some other language that reduces the rate of heisenbugs and they'll have fewer features that "deteriorate" in this way. Also I should buy a new phone at some point.