Related to #2390, apparently the plater, when STL export is run, is putting some parts in the air for the STL export. Gcode export and toolpaths seem to be behaving just fine.
From the linked STLs, I did perform a cut to remove the bottom .2mm (and rotated bracket2B.stl to put it flat against the bed). bracket2B-allplate.stl is the exported STL from slic3r.
Fixed, thank you.
Bugfix: objects were not aligned to Z = 0 before exporting STL from p…