Game crashing all the time / PC freezes sometimes

Since about a month I have the problem that a game (Grand Theft Auto V) is crashing all the time. Sometimes the complete PC freezes too so that it displays the old image e.g. a few minutes ago (completely unresponsive, only restarting the PC helps). The time is not predictable, when it crashes. At one time it crashes after five minutes, another time it crashes after half an hour. But one thing is sure - it will crash.

I have contacted the Rockstar Support and they say they can't help me anymore. Things I did asked by the Rockstar Support:

• reinstalled the game and Social Club multiple times
• deleted game files in AppData/Local/Rockstar Games/GTA V and Documents\Rockstar Games\Social Club
• deleted C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\GTAVLauncher.exe and restored via Steam option Verify integrity of game files
• DISM.exe /Online /Cleanup-image /Restorehealth and sfc /scannow multiple times
• uninstalled another app, which should be responsible for network timeouts/blocking
• switching to story mode/second character
• submitted the export of msinfo32 including crash reports to the support
• changed firewall settings

Things I tried myself:

• played in Safe Mode
• changed graphics settings
• removed OC
• updated to latest Nvidia driver (436.15)
• updated Windows 10
• checked the event log, but there is no entry
• executed memtest86 without problems
• made a stress test with FurMark without problems

I don't have expierenced similar problems in other games/apps.

System configuration:

• i5-6600K
• 16 GB RAM
• Nvidia GeForce GTX 780

Temperature is always OK.

Launcher.log from GTA V writes something like:

Reset failed with D3DERR_DEVICELOST. 
Game exited with code 0xc0000005 
Category:  5 (ERROR_CATEGORY_EXIT_CODE) 
Code:     -1073741819 (c0000005) 
Exit code 0xc0000005 indicates a game crash (STATUS_ACCESS_VIOLATION) 
Unable to clear in-file and out-file!

How can I find the cause of this error?