Holes through base layer ignored

[locoman 0]

I have two small stl files which CURA complains that they are ' not manifold' on loading for slicing but slices anyway. On printing small holes wanted  through the base layer are ignored and printed filled in. (I have checked the CURA setting for mesh and holes)  Other holes in other locations printed OK.   STL files were produced by TurboCad  Pro, am using CURA 4.6 on windows 10 64 bit. One  example stl file is attached

Alice handrail knob sliced.STL

[kbcjeremiah 0]

I have a similar problem, but with large openings in the base layer of my model showing in the solid view but being ignored by slicer (Cura 4.6, Windows 10 64, Creality CR10/Ender 3).  Remainder of print is fine.  STL and 3mf files attached.

CCR10_first floor 2.3mf first floor.stl