GamePress - Why are Moveset Rankings different on your mobile app?

GamePress - I find discrepancies between moveset rankings on this web site and your Godex mobile app.
Example: Golduck - Attacking Movesets:
WG/IB: Web C; Mobile D
C/HP: Web C; Mobile F
C/IP: Web D; Mobile F
(50% of the attacking movesets have different rankings on the web site than on the mobile app in this case.)
Why?