Illustrator CC 2020 (all releases) | Illustrator CC 2021 (all releases)
Mac OS Catalina 10.15.7 and higher - Windows 10 (all version supported by Illustrator)

Hello community,

I’m writing to you to ask for your help or advice on a problem I’m facing in Illustrator.

We use Illustrator a lot in the fashion industry to draw flat sketches, among other things.
One of the drawing techniques we use is symmetry using an effect created in the Transformation panel (Effect/Distort and Transform/Transform).

When this effect is applied to a group containing paths, it regularly happens that one of the symmetrical parts of the sketch does not appear when printed or when the sketch is exported in pixels (jpeg or png).

This problem is a regular occurrence and very frustrating.
Do you know where this bug could come from and are there any workarounds?

Note: using the new symmetry function is not the solution, as it does not allow overlapping paths to be displayed (any path that exceeds the axis of symmetry is not displayed). The tool is therefore very limited and does not respect the symmetry principle correctly.

Please find attached an illustrator file and some explanations about the issue.

Thanks for your help.