Cura 3.1.1 strange support artifacts

[pieri70 1]

Hello

I'm learning using Cura, I'm on MAC and I'm trying to slice a multicopter frame which has many hanging parts so it needs a lot of support.

I configured Cura so it generates support but there is a strange thing occurring

In areas without hanging parts Cura generates a lot of support small islands, so my printer moves a lot around without need.

This happens for 5/6 layers (0,15mm layer height)

Why is this happening?

I thought it was a damaged stl file, but I passed it trough netfabb online repair tool and nothing changes..

 

Here is a snapshot

Thanks

[pieri70 1]

Here a particular