I think I may be having a related problem.
I’m creating a bulk importer to take youtube videos and bring them as oembed fields in standard wordpress posts.
I’ve done the process manually from the admin using a field group that I put together.
When I attempt to use the REST API via a Python application and make my http post requests to create a new wordpress post, I get a new post but the ACF field group is null in the acf object.
I was hoping that this was not a problem given that the recent updates to the REST API sound like this ought not to happen?
I’m having a very similar issue. Did you find a solution?