On our custom post type, any ACF Radio Button or Button Group is not saving its state.
For example, we have a Button Group with two choices, A or B. If the user selects one and saves the form, the data is saved. But, when the user goes back in to edit that form, the states of those choices are null (all choices are un-selected). Updating the form now saves those button values as null.
I should note that we do have “allow null” but need that to be the case.