The main game and hearts of stone were running very well on 1.12 with stable FPS at 30 (except some regions on skellige with lots of foliage, where frames dropped partially to 25) but nothing to worry about. Overall a very good and "fluid" performance

With patch 1.21 the FPS go partially down to 5 FPS (stutter) in some areas in toussaint and novigrad and it doesnt really matter if on "ultra" or "low" - there are just occasions where the FPS drop below acceptable values and video stutters from one second to another for no noticeable reason.

For me its unreasonable to get a new gpu accelerator that drives the game with 72 fps most of the time just to avoid the below 24 fps on some occasions - it was everything fine with 1.12 / on 1.21 areas once fluid stutter

Makes it for me a real gamebreaker not to mention all the other known bugs

EDIT: not using GOG galaxy

Same here, start new game and get crazy stutter/audio skipping, especially the first village.
That should not happen with an i5-4590 and a GTX 960

I beat the whole game last year with the same computer, no problem.

I've got a GTX 970 and most everything is maxed and I get 60 almost constantly. However, I set background NPC to low (they get in the way anyways), grass foilage to medium, AA for hairworks OFF but leave the prest on high, ultra texture, high water, etc.

Amazingly the game doesn't use much VRAM, but it CAN use a TON of actual RAM. There's a memory leak and I went from 900mg at game start to now 2.5GB just getting the game on. In an hour, it'll be 3-5gb, and yesterday it went as high as 12gb. I now have to reset the game every hour to keep the value low.

I would check the RAM usage while game is paused in task manager. If that's not an issue, set everything to low and see if it changes.

Also, if you have your video card settings to (for me, it's the nvidia menu) 8AA, everything on or maxed in global settings, it'll tank games like this. I leave everything sane in global, then adjust actual game tab accordingly. Games like this, forced AA of 4 or higher can kill performance.

Before doing any other investigations, I recommend turning off the GoG Overlay (if you're playing via GoG Galaxy) and going back into the game.

This might not solve it, but I have had some performance and weird stuttering issues in a couple of GoG games which was fixed by turning off the GoG Overlay.

Try that and see if it helps.

New patch equals new bugs.

I also have this issue – 1.21 caused a drop from 25-30 fps to 6-7 fps with no other changes.