I'd have a double check of the limit screws, tension (cable and B) screws and chain length, per Sheldon. If after that it's the hanger and / or the mech' you'll have eliminated those variables:
"Derailer Adjustment" https://www.sheldonbrown.com/derailer-adjustment.html
"Derailer Adjustment" https://www.sheldonbrown.com/derailer-adjustment.html