Hello @matthewlane
From my experience when I work on client’s sites the existing fields stay in place and do not duplicate when importing. However, if you are able to use the Local JSON feature of ACF that would be the best option to sync updated fields between environments.
https://www.advancedcustomfields.com/resources/local-json/
Hello @cpdesigns,
I’ve been recently working on a few projects with ACF and the clients always enter their final data for a page on the staging site and then want to transfer the field data to the production site. The fields were set up the same on production for the new page, but no option to transfer just a single page’s field data.
This became an annoying to do all the time so I created a page migration plugin that will migrate the ACF Field data. I’m still in beta, but I’ve listed the fields I currently support. Not sure if it could be any help. I would appreciate the feedback!
https://github.com/joeshonm/WP-Page-Migrate