Hello niezmywalny,
I recently ran into the same problem after accidentally disabling all the plugins (including WebAuthn and W3TC). I found this was caused by set transient failure with object cache enabled.
I managed to work around by checking “Store transients in database” option, which may harm the performance a little bit but makes everything right. I’m not sure if the problem belongs to WordPress, cache engine or WP-WebAuthn, but I think similar workarounds may be helpful.
