Hi,
It would have been more simple to help if you posted the code you used to get the User field to populate and to disabled/readonly the sub-field once it is saved.
To put you on the path (to be confirmed depending on your code) :
1) Add a specific class to the sub-field in ACF back-end (like “always_disabled”) and add some javascript by using this selector to always disabled the field (see in ACF/WP documentation how to add it properly).
2) Use the “prepare_field”/”load_value” functions to populate your sub-field value (as you probably done) and to set the field to “readonly” (required to avoid weird reaction of ACF when trying to save a JS disabled input)
3) Save the sub-field value by using “update_value” / “save_post” or other function (because the disabled and “readonly” sub-field will not be saved automatically).
It is not necessarily the ultimate solution, but it’s work for me. Hope it helps, send you code if you want more details =).
