I have a similar issue and any help would be greatly appreciated.
I also do not have any caching plugin running and am using ACF Pro 5.5.10.
The bidirectional update seems to be working and when I add a CPT to the first field and save I can go into the edit screen for the that CPT and see that the second field is updated.
The problem is that when I go to the template (that uses the second field) there is no data coming through for that particular field. If I return to the admin and update the CPT (and the second field) on returning to the frontend I can now see that there is data coming through for the second field?
Not sure why this would be happening as the update_field code appears to be working correctly as I would not see any CPT’s in the second field if it wasn’t.
Is there some step in the update process that isn’t running?
