Guide

A Flow is overriding your lead assignment rule.

The assignment rule looks right, the lead still ends up with someone else. When that happens, a flow is usually changing the owner after the rule has decided.

The order Salesforce runs things in

On save, Salesforce runs before-save flows first, then the assignment rule, then after-save flows. So an after-save record-triggered flow that sets OwnerId overrides whatever the rule chose.

What to look for in each flow

• An owner set after save. Any Update Records step on the lead that writes OwnerId in an after-save flow.
• A hard-coded owner Id. A step that assigns to a literal user or queue Id. When that person leaves, the flow keeps assigning to them.
• No fault path on the owner update. If that step fails, Salesforce rolls back the whole save. A web form lead can be lost with it.
• Steps nothing leads to. An old round robin left in the flow, with no connector into it, never runs. It still reads as if it does.

Check it yourself

In Setup, open Flows and filter to active record-triggered flows on Lead. For each, note whether it runs before or after save, and open every step that updates the triggering record. Then take one misrouted lead and read its owner history:

SELECT OldValue, NewValue, CreatedById, CreatedDate FROM LeadHistory WHERE LeadId = '00Q...' AND Field = 'Owner'

An owner change in the same second the lead was created, by the user who created it, is almost always automation, not a person.