I have the exact same issue on an Asus laptop. I was confused for days because I got hibernation working, and then I did a few tweaks… and it broke, I tried to undo all the tweaks I could remember, but after hours of trial and error, it was still broken.
Then I noticed that if I press Hibernate from the system menu, it works.
At first I thought it was just random, maybe it works sometimes?
But after testing more, it was consistent: It always succeeded if I pressed the Hibernate GUI button, and it always failed if I pressed the keyboard Power button.
That’s when I remembered that I had changed the behavior for the Power button from Show Logout Screen, to directly Hibernate. I just never thought that could be the issue so it never occurred to me to try and revert it.
…after searching around for a bit, I got this suggestion for cause, but I’m not knowledgeable enough to verify it it’s correct or just speculation:
“PowerDevil receives the button press and initiates a “Lock & Hibernate” sequence.
The Screen Locker (kscreenlocker) attempts to lock the session simultaneously. This could create a conflict where the driver tries to save VRAM while the screen locker is trying to redraw the UI.”
Skimming through the logs does indeed show Nvidia failures and wakeup events, followed by repeated systemd memory dump attempts and other failures.
It’s 100% reproducible, and it only happens if I configure System Settings > Power Management > When power button is pressed > Hibernate. As long as I leave it on the default value “Show logout screen” everything works smoothly as it should.