SharePoint Search returns people based on name of Distribution List of which person is a member

In SharePoint, doing a search for 'Education' for example.

Results include people who are members of an Exchange Online Distribution List (DL) whose name includes 'Education'.

Nothing on the user accounts themselves refer to 'Education' - it is literally only that the people are members of the DL.

Testing in a different tenant, I am able to reproduce it, and indicates that it is specifically DLs affected - not Security or M365 groups

This is reported by my customer to have started occuring in the last 2 weeks.

No relevant config changes have been made on the customer side recently.

Anyone got any ideas whether this is a recent change, and if so, where it is documented?