While in a trainer battle the opposing Kyogre was able to use water spout despite my primal groudon standing on the other side apllying its desolate Land abillity.
My Groudon wasn´t the pokemon to start the battle. I switched it in once before against another pokemon, then out and later back in against the kyogre predicting a water move.

Hi there, sorry about the late response on this one!

I can confirm on the latest release 9.1.2 that Kyogre and Groudons weather abilities seem to be setting the regular variant of the weather, rather than their stronger primal variants. This allows the use of water moves under desolate land, which should not be happening. Moving to the internal tracker to be fixed, thanks!