Before I discuss the log.txt file when was the last time you upgraded your graphics card driver? I would suggest you upgrade if you haven't done so in recent times.
I would also suggest running the installer program. In doing so it should add any files that are missing and or replace X-Plane files that are corrupted.
Then run your system to see if the problem is solved
I am a "long way" in being an expert in reading the log.txt file.
I was unable to find any indication causing the cloud problem.
However some observations I have deduced from the file script.
1. It is one of the longest files I have perused without a lot of add-ons or plugins.
2. My presumption is your preferred aircraft for flying is the Flight Factor A320
3. The script advises that you have a number of aircraft loaded that are no longer supported as indicated 0:00:13.876 W/ACF: Scanning of aircraft files is complete. Some of your aircraft files will not be available to fly in X-Plane, probably because they were created by a version of X-Plane that is too old. Aircraft that will be ignored: 0:00:13.876 W/ACF: Aircraft/Mediocre planes/ATR 72-500/ATR72.acf
4. Also script indicates that your version of the A320 aircraft is not supported or out of date. If you have recently purchased the aircraft you need to determine if it has been updated for XP11 Although I am of the opinion the type of aircraft should not effect the out of cockpit visuals I would suggest temporarily moving the A320 directory away from the XP directory and select another aircraft. to ascertain if the problem is solved.
5. I am aware that to run some plugins the FlyWithLua file(s) are required. Script also suggests to me that you may need to update the FlyWithLua file/version. My reading of the script suggests this is causing problems as well.
Hope the above is of some benefit.
The worst case scenario is to move the full "plugins directory" out of XP then run XP to determine if the problem still exists. If it doesn't then progressively add each plugin back until the problem starts again.