Roy & CruxOp - If you email me I can get into more depth with trying to troubleshoot the problem. Really sorry for getting back so late! I’m much quicker with emails. I think what the problem is has to do with the spawn height/angle OR the collision on your landscape mesh.
If it’s the spawn height or angle it’s simply a matter of either changing the in world height of your landscape mesh to be < 10000 & > -10000. Alternatively you can change the min and max ranges for that. These would be located in the structure template’s blueprint. The second half of this problem would be the spawn angle. If you’re trying to place an structure on hills and valleys you will find some trouble unless you change a setting in the structure template blueprint. When checking if placement is OK, the function will return false if the angle is greater than a certain amount. For demo purposes this is perfect but I know that developers would certainly want to have diversity to the angle of their maps. I detail exactly how to change this in the documentation.
As for the second possibility, it’s much more simple. If your landscape mesh doesn’t have visibility and collision setup properly the trace for setting a structure will not register your landscape. I’m assuming this is not the case (as you’d probably have figured that out by now) but I like to include that as some users have solved this problem by fixing either visibility or collision of the landscape mesh.