When I view a customer's contact card, it show only their tickets:

When I go to the same customer's ticket, the smart button shows multiple tickets:

Clicking on the smart button shows multiple different customer's tickets:

The only relation that I can find between the "linked" tickets is that all of the customers email address use the same domain (c1@example.com, c2@example.com, etc).

EDIT:

There is something wrong with this specific @domain.  Deleting the email address removes the customer from the other linked tickets.  Adding their email address back adds them back to other linked tickets.  Creating a ticket with a different customer with the same @domain adds them to the other "linked" tickets.  No other @domains seem to be affected.  Bug?

V16 Odoo.sh