Would this be an Apple Lightning to Digital AV Adapter, or a third-party alternative?
Your Power Adapter needs to be rated at 12W (i.e. 2.4A @5V) or more to successfully charge your iPad via an Apple Lightning Digital AV Adapter.
If charging issues persist, try substituting the Power Adapter and Lightning charging cable.
If you are unable to resolve the problem, you would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to hands-on test and assess your iPad, AV Adapter, Power Adapter and charging cable(s):
Genius Bar Reservation and Apple Support Options - Apple