Dependent Dropdown List Filtering Doesn’t Restrict Options

Issue:

The dependent dropdown list shows all options, regardless of the values in the controlling field.

What to Check:

Is the dependent field a List/Record custom field that points to a custom record type (not a custom list)?
Does the custom record type for the dependent field have a field referencing the controlling value?

How to Fix:

Use a custom record type (not a custom list) for the dependent field.
Ensure that the custom record type includes a field that references the controlling field.
Ensure that each instance of the custom record type has a value filled that references one of the options of the controlling field.
Set up filtering using the Filter Using option and verify correct configuration.