erratic behaviour while creating a new mission

Hello.

I am creating a new mission as usual for a mini 3 pro.

I have to keep pressing the finger to get the starting point, then keep again the finger pressed in order to define the first 3 point and then I see the path of the flight.

From this point I am stuck. I am unable to move the small dot between tha created points in order to create a fourth one. 

Instead of seeing the line moving, I have the whole map moving.

So I am stuck with a triangle shape and cannot define any other boundary point.

Tried to install the app again with no result.