Hi there, sorry for the delay! We're currently working through older tickets, and upon testing this issue, I can see this is still occuring in the current version (8.3.6).
My testing method:
1) Gave myself a Venusaur with the move Weather Ball. Gave Venusaur 10 Dynamax candies, and equipped a dynamax band to myself.
2) Set the weather to rain in game.
3) Engaged in battle and dynamaxed, using Weather Ball (which, as is normal, becomes Max Strike).
4) According to Bulbapedia, this move should say "Max Strike" but instead do whatever actions the corrosponding weather dictates - as it was raining in game, the move should have had the effects of "Max Geyser"(creating rain for 5 turns), but instead had only the effects of Max Strike (does damage and decreses the enemy's speed).
As such, I'll move this issue to internal; thank you!