3 Copies of same object, but one missing elements on first layer when after slicing

[BradLevy 4]

With Cura 4.8.0, I have several models with which I'm seeing the same odd behavior.

 

When I place the model on an empty build plate, some elements of the first layer are missing when sliced.

If I multiply the model (place additional copies) on the build plate, the elements show up in the addition copies.

Any idea what could cause this?
Example shown below. The first instance of the model (on the left) is missing two diagonal elements from the center circle to the x and y vector elements (also missing) which tie them to the periphery elements. The slicer does extrude those elements on the two additional copies on the build plate.

[BradLevy 4]

Here is a simpler version of the .stl file, showing the same problem when sliced.

The elements that are being omitted (not extruded, even though movement made along their path) are 0.5 mm thick. Slicer settings are for 0.2mm layers, so they should be several layers thick. I've tried with and without adaptive layers checked.
The model consists of two bodies in the CAD program:

(In this screen cap, I selected one of the two bodies so it would show up a different color in the capture. Note that the missing elements are part, but not all, of one of the two bodies. The highlighted (brown) body exists to provide better adhesion during printing, keeping the four sections of the part shown in blue together and better anchored to the plate. (There is more going on higher up in the original model, but I truncated it to the few mm high in this version because they don't affect the buggy behavior in question.)

slicebugcheck.stl

Edited December 18, 2020 by BradLevy
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[Cuq 198]

It is not a question of layer thickness but of nozzle size and line width ... We do not have any information about nozzle and line width. It would be more efficient to share your project instead of the STL file.

 

My point of view wtih the actual information : The dimension of the grey element are equal to your nozzle size = 0.4 

You can reduce the line width to  0.35 or change the geometry of the grey element. 

 

If you reduce the line width take care of the parameter : "Outer Wall Inset"

[BradLevy 4]

Thanks. The width of those elements is 0.4mm in the CAD program. But I can understand how dimensions that display as 0.4 may actually be ever so slightly smaller as a result of limitations of internal representations and finite precision math. (Some numbers can be exactly represented in a fixed number of digits base ten are repeating decimals in other number bases, and vice-versa.) The elements appearing/disappearing in different copies on the same build plate/same settings are probably the result of placement transformations throwing tiny difference between the actual width and 0.4 mm back and forth between below and above 0.4 mm.  On seeing your comment, I did some experimenting with line width and the Outer Wall Inset parameter. When I changed the Line Width in Cura to 0.39 mm, the Outer Wall Inset setting went to 0.005, and I still had some missing elements. But changing the Outer Wall Inset to 0.0 (while leaving line width at 0.39) caused them to show up.  They also showed up with the combination of Line Width = 0.4mm and Outer Wall Inset = -0.01.

One computer language from my youth, APL, had a comparison tolerance setting that controlled how close (in relative terms) two numbers had to be to be considered equal - useful for decisions in calculations like these. Cura might want to use some similar logic.

When I further increased the number of copies (with the original Line Width and Outer Wall Inset settings) some of the similar elements were missing in some of those copies as well, further refuting my initial thought that it had to do with first vs successive copies of the model.

Anyway, thanks again. Glad I can now print the model with the additional elements present. They are significantly helping the success rate printing small-footprint items in ABS.