Firstly, please make sure that your PC meets the GWENT System Requirements.
If the requirements are met please make sure that all applications non-essential for playing the game are turned off/disabled. This includes antivirus/antimalware programs.
If that won't help please check if your PC is malware/virus-free - those may sometimes cause crashes.
You may also try verifying game files.
1. From the Library section, right-click on the game and select Properties from the menu.
2. Select the "Local files" tab and click the "Verify integrity of game cache..." button.
3. Steam will verify the game's files - this process may take several minutes.