This article applies to Magics 27 and 28.
Thickening of the non-solid support might create open contours for some geometries. This can create empty slices for supports while slicing with some Build Processors (Concept Laser 1.2, Sodick 1.0, Additive Industries 2.6)
Solution:
Regenerate supports
In Magics 28.02 and later versions issues with open contours while thickening the non-solid support are being fixed, there is a high chance a regeneration of supports (Regenerate 2D & 3D) in SG mode will fix the open contours issue.
Set a larger "Maximal gap size"
In Profile editor of the BP, make sure you have "Enable gap fill" checked and try to increase the value of "Maximal gap size". Increasing the value might help account for the gaps created by the open contours of the thickened non-solid support.
Workaround
Fix the thickened support in Magics.
When using thickened support, set the parameters in Machine properties to convert solid support to .stl. On exit from SG mode, check the "planar holes" in the Part fixing info and run the fixing.