After upgrading to v0.18.1 I can't connect from 2 of 4 machines (that I checked so far).
The users that can't connect are relatively new and where created with the v0.17.0 server / clients.
When trying to re-set the password I get:
$ kopia server users set root@machine --ask-password
Enter new password for user root@machine:
Re-enter password for verification:
ERROR error setting password: unsupported hash version (0)