Incoming new emails from different senders are being associated with existing old tickets/threads from 4 years ago. Ticket shows threads from unrelated departments.

The cause is that ost_form_entry rows were imported from an older osTicket instance into the current one. The object_id values in those imported rows collided with current ticket_id values, causing form entries from old tickets to attach to new ones. Never import individual tables across osTicket installations -- always migrate the complete database or start fresh. If AUTO_INCREMENT IDs are colliding due to MySQL < 5.7.5 not persisting the counter, fix with: ALTER TABLE table_name AUTO_INCREMENT = ;