Field isn't an option for conditional display filter on a LEX page?

Any @Salesforce.org System Administrators​ know what is happening? Working on the Case Lightning Record Page in the repo of the @Community Project - Ombudsman Cloud Care​ app. Trying to add a conditionally displayed component based on whether the Sailor field on case is filled or not. But the Sailor field (which IS on the page layout, IS available to me as sysadmin by FLS) does not come up in the filter choices, either directly on the field picker or on the Advanced picker. WTF??