I only bought and play this game because plenty of RPG lovers said it's one of the best games ever made in this genre. But GODDAMN, this game is a pain to run on modern rigs. Crashes every hour and a half, probably because of the Widescreen fix (which is already a pain to get working; have to run the game up to 8 times in a bad day just to get it working), after-combat movement problems, constant save-file corruption and other minor things contribute to just completely shatter any hope I had in this game. It just takes one back-luck moment where your character gets stuck after a combat scene, followed by a bad-luck moment of quick-saving>quick-loading to get your save corrupted and lose the last half 20 minutes of progress. I would have no problem playing without the Widescreen fix if the text scaling wouldn't obstruct you so much when you try to click on things. It's pretty invasive, without mentioning ugly.

It's already pissed me off to the point I don't even want to launch the game.

Okay, rant off.

Well, that's obviously not normal.
I am running the game flawlessly, without a single crash, on multiple machines and operating systems, now and in the past.
The widescreen fix is stable as well.

I am really no expert by any means, but could it be an issue with your hard drive?
Some basic information is needed to help you, like OS, specs (especially graphics card), game version and stuff like that.

Crashes every hour and a half? Which means it runs just fine for an hour and a half? That is not the game, nor the widescreen mod. That is something on your system. Prime suspect: background tasks. Maybe overheating? Check your RAM and open up the box and clean it with a can of compressed air -- do NOT use brushes or vacuums because of static. Dust bunnies can be a real cause of overheating, as can physical positioning of your box. Make sure it has plenty of air circulating around it, especially the fan vents. And kill those non-essential background tasks. Even disable your security software, at least for troubleshooting. Also, never forget the one thing that most people overlook these days: reboot your computer regularly.

I got a high-end PC able to run Witcher 3 maxed out at 60fps for hours without crashing. Every 3 months I dust my PC. Every year I reinstall the OS. Every night I turn it off. No, I really don't think it's hardware, everything else works perfectly (every game well-optimized, that is).

Isn't there a way to verify file integrity like in Steam? I'm 100% sure it's software, not hardware.

I said it was software (prime suspect). Have it your way if you can't be bothered to read.

As Hickory wrote, check for any applications or processes that might mess with the game.
You seem to take good care of your computer, yet you keep playing a game that crashes every few hours....

I did read your question and I also read Umoev's. I was replying to both of you. I take care of my PC, so it ain't hardware. I have already tested running the game in the background, yet it still has problems booting up the Widescreen fix and still constantly corrupts save files.

So I ask if there is a file-verification tool, like Steam has.

You didn't read my reply at all. Or at the very least, you failed to understand what I was saying, going by your both replies.

Maybe this is simply a communication issue.
Okay, we can rule out your hardware. when you don't have any other issues with your system, especially when playing other games. That makes it a software problem.
"Background tasks" doesn't mean running the game in the background, but checking for other processes that might interfere with your game's. For example, there are quite a few games that have problems with the communication software Skype, they won't run correctly if Skype runs in the background. There are some cleaning utilities, virus scanners, even some Windows services that could mess your game up. You should start your Task Manager before starting the game and look for those, terminate them, then start the game.

As far as file verification goes, there is an option to test the integrity of the installer when installing, but otherwise... I could provide you with the about 15000 MD5 hashes of the game files from my working setup, if you know how to check that.

Nevermind, didn't realize my "fix" is standard in the GOG version.