This is a known UE4 issue, but I also experienced the issue recently in a game built on Unity which leads me to suspect that part of the problem is with recent Windows 10 updates and/or Nvidia driver updates.
See the link and try the tdr registry settings fix in the comments at the bottom of the page, although this didn’t fix it for me but only made crashes less frequent.
Try lowering your main RAM timings if it’s OCed not GPU memory timings. Set your RAM to base timings and GPU also. Run the game and see if it still crashes. If it works, then start raising your OC and testing until some point where 3D graphics are still stable.
This has seemingly fixed the issue for me. The last two Conan Exiles releases haven’t crashed in several hours of game play. Personally, I think the recent Windows 10 updates changed something that made previously stable overclocked memory unstable when 3D graphics are loaded. But I can’t prove it.