I stumbled upon a rendering issue with the ray tracing renderer. When I turned on the ray tracing, the edges of my 6 layer board looked kind of sketchy and one was even completely transparent. I tried to reproduce the issue with a minimum of components.
1) I can't reproduce the same effect
2) Something else happened - one board side has a black king of overlay
3) It only seems to happen if the board has more than two layers
I left the settings for the ray tracing renderer "as is" and only disabled "add floor" but this particular setting makes no difference. I attached some screen shots and my minimum (not) working example. Some people from the forum confirmed that they also see the issue (https://forum.kicad.info/t/transparent-board-edge-with-ray-tracing/19857/4).
I can't share with you the board file with the transparent edge because I'm working under an NDA but I will try to help as best as I can.
Application: KiCad
Version: 5.1.4-e60b266~84~ubuntu18.04.1, release build
Libraries:
wxWidgets 3.0.4
libcurl/7.58.0 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
Platform: Linux 4.15.0-70-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
Boost: 1.65.1
OpenCASCADE Community Edition: 6.9.1
Curl: 7.58.0
Compiler: GCC 7.4.0 with C++ ABI 1011
Build settings:
USE_WX_GRAPHICS_CONTEXT=OFF
USE_WX_OVERLAY=ON
KICAD_SCRIPTING=ON
KICAD_SCRIPTING_MODULES=ON
KICAD_SCRIPTING_PYTHON3=ON
KICAD_SCRIPTING_WXPYTHON=ON
KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
KICAD_SCRIPTING_ACTION_MENU=ON
BUILD_GITHUB_PLUGIN=ON
KICAD_USE_OCE=ON
KICAD_USE_OCC=OFF
KICAD_SPICE=ON
Screen shot of the "reproduced" issue.