I've noticed that if a part is placed flat to the build plate at 0.00 lift and supports added , no first layer is generated (even for the added supports.
Background:
I am trying to make accurate 'square' parts , so i usually add addition support to the model in CAD before transfering to slicer . The support parts will be cleaned off after printing.
I recently built parts with support that could be built straight off of the build plate (to avoid the typical rough hanging edges) . These were placed on the plate at 0.00 height and a few addition slicer supports added where necessary.
The print failed. On printing a second time, I noticed that the first layer did not appear in the preview window so aborted the print.
On inspection of the sliced models in CB , the first layer of the parts was not generated at all , even the foot-prints of the CB additional supports were missing.
Bill