One minute video to that problem: https://streamable.com/2zo4sx

- the main character disappears when climbing in a cave, jumps on steep slopes.
- he stumbles in the air or stands in the air when falling down, falls into traps. ("airwalk" exploit)
- too frequent thunder, weather doesn't want change, it's always raining.
- strange camera movements, delayed camera tracking.

The solution is to lock the FPS under 90. Either by nVidia or AMD settings.
But setting the FPS Limit through RTSS always works. (download links at the very bottom), like in the video above, or attachment below:

Another solution if you have an nVidia graphics card and your monitor has 120 Hz, 144 Hz, 165 Hz or 180 Hz refresh rate.
(only PC's, not for laptops that also have integrated graphics, you don't need RTSS for this)

1) right click on desktop
2) nVidia control panel
3) Manage 3D settings
4) Program settings
5) Add: Risen.exe
  (C:/GOG Games/Risen/bin/Risen.exe)
  (C:/Program Files (x86)/GOG Galaxy/Games/Risen/bin/Risen.exe
6) Vertical Synchronization: "Adaptive (half refresh rate)"

What does it do? It removes the bugs mentioned before. It's an alternative way to limit the FPS below 90. If you have a 144 Hz screen, the game runs with 72 FPS. If it is a 165 Hz screen, the game runs then with 87 FPS, etc.
So if you have a 60 Hz or 75 Hz monitor, you only need to set Vertical Synchronization: "On"

There's already a new method, just use this FIX:
"Risen FPS and Aspect Ratio fix".
https://www.moddb.com/games/risen/news/risen-fps-and-aspect-ratio-fix-10-released

which removes the disappearing problem when climbing. And lowers down the mouse sensitivity at the same time.

I didn't encounter the character disappearing when climbing ledges, but I remember the air walk bug and the stretched screenshots. Thank you for the link.

This is going to fix disappearing character when climbing ledges and air walk, but it's a software hook that can easily cause perfromance issues and AVs. It's better to use the previous solution of setting VSync and/or capping FPS via graphic card's control panel (capping FPS around 80-90 should work even for 120+ Hz monitors in fixing these bugs). It works for nVidia and AMD too, if you know how to set up profiles for Risen.exe (tested myself).

Setting FPS limit to 150 is enough to fix the problem for me. I use dxvk environment variable on Linux:

DXVK_FRAME_RATE=150

With the newest patch from January you don't have to limit the framerate to maximum of 95 FPS. But there's still a problem with the too frequent lightnings during a stormy weather.