As pointed out by @Luksprog in a comment, you need to change
getActivity().getSupportFragmentManager()
for
getChildFragmentManager()
Why: getSupportFragmentManager()
(and getFragmentManager()
) is used to interact with fragments associated with this fragment's activity, which is not what you want.
What you want is to place and manage Fragments inside of this Fragment (using your adapters), which is the description of the getChildFragmentManager()
method.
A big thanks to @Luksprog for the pointer; I had the same problem you did, and he had the answer! Just posting his answer in a real answer, for others who might not think to look in the comments for an answer to this issue.