The Instant App Social media share button doesn't work if the web map consists of "too many" layers (so far I have been unable to ascertain what the limit is).
You can add the button to the app, but when the user clicks on it, nothing happens.
It would be a better UX if the builder stopped you adding the share button to an app that is too complex for it to cope with. It would also be helpful if this limitation was documented.
Thanks,
Sarah