Hi Kourmpanas,
Just to check, have you added a navmesh to the level? Also can you post some screenshots of your behavior tree and the blueprint of the task?
In your node for Get Random Point in Radius, what is the radius set to? You will want that to be quite high (something like 2000). Is the variable for the location exposed and being passed to the Blackboard? Any addition information may help resolve this issue. I would also suggest taking a look at this tutorial for more information:
Thank you