I cannot reproduce this. If you can, save a MINIMAL (to make it easy for us) PLN file, zipped, on a download site such as dropbox that contains just the element that is showing the problem - and so that the 3D view that any of us will get when opening the 3D window is what shows the problem for you.
Then, one of us might be able to determine if it is a setting, or your graphics card.
Have you tried the various OpenGL options for the 3D window to see which option change makes the problem go away?
r-interface-reference/dialog-boxes/open-gl-options/
PS The reason I ask for a minimal PLN rather than an MOD is that we must have your attributes to have the settings for the material showing the issue and attributes are not included in MOD files.
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB