I've manually set temporary passwords for all of my attendees through the CMS interface, but some of my attendees cannot login with them. Why is this happening?

The passwords set through the CMS when password reset is enabled, are temporary passwords, just like the ones that are sent through emails. All temporary passwords have an 24 hour expiry so it may be the case that some users have not tried to login with the temporary password within 24 hours of the password creation.