Problem bracket

Cannot generate correct gcode for this stl file with sf35.
I tried different settings but there is always a problem, either with an incomplete layer or printing in the air. These problems are reproducible: you can see that the gcode is wrong when using a tool such as Pleasant3D.
When I accidentally made the hole in the object too large (first attempt) there was no problem. When I lay the object flat on the base for printing (rotate in repG) there is no problem but the object then lacks strenght.
When I remove the hole (in Sketchup) and print the object without hole there is no problem either...