Why is Safari locking up when I use a passkey?

I am getting increasingly frustrated by the number of times that Safari locks up when trying to login to a site using a passkey. It's not all sites. Some always fail, others occasionally, and the rest not at all.

The symptoms are that the passkey box pops-up, I enter my password, but the box just refreshes. Cancel doesn't work and the only way out is to Force Quit Safari.

This is with version 26.1 on a Mac running Sequoia 15.7.2