Third level field doesn't show the options to choose one.

Problem/Motivation

I have a content type with four entity reference fields pointing to taxonomies.

The fields are:

• Degree type, referencing the degree type taxonomy, limited to a single value.
• Degree subtype, referencing the degree subtype taxonomy, also limited to one value and related to degree type via an entity reference field called field_related.
• Degree area of study, referencing the degree area of study taxonomy, limited to one value and also related to degree type via a field_related entity reference.
• Degree standard name, referencing the degree standard name taxonomy, with unlimited values, and related to degree area of study via a field_related entity reference field.

When I create a new content item and select a Degree type, the options for Degree subtype and Degree area of study are correctly filtered and displayed.
However, when I select a value for Degree area of study, the Degree standard name field shows no available options.

I have verified that all taxonomy terms are correctly related to each other across the taxonomies, and there are no error messages in the logs (watchdog).

The same view is used for the three fields (subtype, area of study, standard name), but with three different displays.