This is a warranty issue of which Walther is aware, if its in warranty return it to the supplier and get them to take it up with Walther, if they fail too, contact Walther service dept, direct in Ulm.

The problem is a rocking movement of the steel insert in the grip, which is held by an allen screw. On later versions Walther resolved it by not having that steel insert removable and have bonded the insert into the wood grip as well as the screw. If its in warranty, and in some cases out side warranty they will replace the grip with the revised bonded one.

OR, you can remove the steel insert, drill or grind relief in the wood, then use an apoxy resin (araldite works well) use a lamp bulb to warm the joint so the resin flows well into the joint of steel to wood. When it drys the problem is resolved.