Ticket links sent to end-users intermittently redirect to login or ask for email and ticket number instead of auto-authenticating.

Enable the auth token setting: Admin Panel > Settings > Tickets > enable the option that allows unauthenticated access via token. This is a known Guest User session issue in v1.18.3 (reverted from v1.18.2 fix). Clearing all browser cookies and cache resolves it temporarily. The underlying Guest User session bug is acknowledged and planned for a future fix.