If you're saying you receive an error message upon crashing, simply send that into CDPR Support with an explanation of the issue:
https://www.playgwent.com/en/contact-support
Exit issues are normally down to drivers, Windows security and permissions, or 3rd-party software, and it will vary from one system to the next.
1.) Be sure the game and galaxy are not installed anywhere under
Program Files or
Program Files(x86), and set the .EXEs to "Run as administrator".
2.) Edit Permissions for both installation paths and set them to "Everyone".
3.) Install / repair all Microsoft Redistributables, especially Visual Studio 2013 and Visual C++ 2013 (both the x86 and x64 versions of each).
4.) Disable anti-virus and see if the crashing stops.
5.) Verify / repair the installation through Galaxy.
6.) If all else fails, try reinstalling both Galaxy and Gwent to different installation paths. (Again, on the root of your drive in a folder of your own creation.)