Problem:

Are you attempting to use Field Options Sync while depending on other issue values to build the resulting list?

Cause:

Select-list custom fields in Jira cannot depend on other issue values due to their inherent nature. These custom fields always require complete knowledge of every possible option that can be presented.

Workaround:

To circumvent this issue, consider using Search Fields. These virtual fields can have dependencies, but they have their own set of limitations.

Tutorial:

How to create tow nested Search Fields