I think the core issue is when dealing with pure local json fields and calling get_field() by name will attempt to check postmeta for the field key. If you call get_field() using the field key, it pulls from local JSON just fine. The solution was looking through local fields for a match – not perfect but works in my usecase:
https://support.advancedcustomfields.com/forums/topic/local-json-get_field-returns-only-using-key/#post-63051
