Edit: Had not seen the parts of the thread regarding object-object occlusion. I'll keep this in mind next time I log in.
I booted into Windows 10 for the first time in months and let it do all necessary updates, drivers, etc. I updated the official LL viewer and NiranV's Black Dragon, both of which I had installed to try EEP before it was available for Linux. I installed Cool VL Viewer for the first time under Windows 10, so there was no previous cache or settings, and no Lua automation script. I did not notice the sky issue with LL's viewer at
https://maps.secondlife.com/secondlife/Clanis/237/34/52. Upon logging in with Cool VL Viewer at the same location, I cammed around using my avatar as the focus point and saw the flashing in the sky once inventory loaded and the scene had fully rezzed.
As an aside, even if this issue cannot be resolved right away, I still enjoy using the Cool VL Viewer.
______________________________
Cool VL Viewer v1.28.0.2, 64 bits, Jul 11 2020 10:32:18
Release Notes
You are at 256749.4, 262178.4, 52.2 in Clanis located at
sim10115.agni.lindenlab.com (216.82.48.181:13002)
Second Life Server 2020-06-12T19:06:40.543526
Release Notes
CPU: AMD Ryzen 3 1300X Quad-Core Processor (3500 MHz)
Memory: 16336MB
OS version: Microsoft Windows 10 64 bits v10.0 (build 10586.836)
Memory manager: OS native
Graphics card vendor: ATI Technologies Inc.
Graphics card: Radeon RX 580 Series
Windows graphics driver version: 27.20.2001.8002
OpenGL version: 4.2.14736 Compatibility Profile Context 20.7.1 27.20.2001.8002
Detected VRAM: 16339MB
J2C decoder: OpenJPEG: 1.4.0.635f
Audio driver: FMOD Studio v2.01.01
Networking backend: libcurl/7.47.0 OpenSSL/1.0.2l zlib/1.2.8
Embedded browser: CEF3 plugin v74.1.19+gb62bacf+chromium-74.0.3729.157
Packets lost: 4/22218 (0.0%)
Built with: MSVC v1916
Compiler-generated maths: SSE2.
Compile flags used for this build:
/O2 /Oi /MP /DNDEBUG /D_SECURE_SCL=0 /D_HAS_ITERATOR_DEBUGGING=0 /DWIN32 /D_WINDOWS /W3 /GR /EHsc /Oy- /GS /fp:fast /TP /W2 /Zc:forScope /Zc:wchar_t- /c /nologo /DLL_WINDOWS=1 /DUNICODE /D_UNICODE /DWINVER=0x0600 /D_WIN32_WINNT=0x0600 /DXML_STATIC /DBOOST_ALL_NO_LIB /DLL_LUA=1 /DLL_FMOD=1 /DAPR_DECLARE_STATIC /DAPU_DECLARE_STATIC /DCURL_STATICLIB=1 /DLIB_NDOF=1