There are many things that can go wrong with the Instagram token generation process. If the token looks good but does not retrieve any media or stories then it seems to be a bug in the Facebook system.
We have successfully worked around this for several influencers by adding a new Admin to the Facebook page that is linked to the Instagram account and then authorising through the Admin's token.
How to do the workaround
In the settings page for your facebook public page which is linked to your Instagram account (see above), go to Page Roles (below).
Add the new user to the page using the 'Assign a new page role'.
The user MUST BE AN ADMIN! (use the little grey selector beside the text box)
Once this is done we can send a magic link to the new admin to fetch the new token.