Right, so then we’ve worked out the following:
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It’s not Grim Dawn at fault, as changing cores/priority has no effect.
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It’s not a driver/USB fault at this point, due to a lack of USB errors and the fact it only happens in GD.
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It’s not a more general Windows OS etc, nor power management based.
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Nor is it the mouse itself due to the same issue happening with a different mouse.
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Only impact on the rate of of mouse cut outs is using older Nvidia drivers.
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Pattern is that it increases with longer time in the game, but this is not effected by frame rate limits.
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Also, mouse pointer isn’t effected, just the buttons, and is temporally sorted via a keyboard button presses
Fuck me, this really is weird. Because in theory issues with the GPU/it’s drivers should not make the mouse stop working, since it should only effect pointer driven stuff. In theory. We’d need one of the devs actually to chime in, but usually in all game engines mouse buttons are linked directly to triggers in the code for skills etc and don’t interact with the UI and the graphics side of thing enough that they should be affected by GPU “fun”.
Anyhow good to see using the older driver worked pretty well and by my potato PC gamer standards I’d call that good enough 
However, there’s some more things we can try.
Like forcing the game to run in DirectX 9 mode:
Which to do, click on GD in your steam library list, right click on it and click on properties. On the first page you’ll see a section called Launch Options which allows you to add flags like you’d also do with shortcuts. Simply add “/d3d9”, sans quotes and try running the game then for testing.
The slightly insane next test is to use a translation layer and run the game with Vulkan: https://www.pcgamingwiki.com/wiki/Grim_Dawn#Anomalous_stutter
Why? Because it’s a known issue with the 5000 series it can have issues with older DX versions, despite Nvidia never having screwed up legacy DX and OpenGL support before. So these two see if it’s just a DX11 issue. And if using Vulkan instead helps, since Nvidia definitely didn’t screw up compatibility for that, as DOOM: The Dark Ages uses only Vulkan 
Blahs, need another coffee, that half a zopiclone I had last night has wiped me out. At lest I’m not spaced out this time 
Oh yeah, need to address this - that sounds awfully like the GPU is overheating. Because one of the things GD is really, really good at is stressing the ever-loving hell out of GPU’s. And unfortunately on the 2000 gen Nvidia decided pushing more power into the GPU was a good idea, so they can run rather hot.
Best thing to do would be to dust bust it and set FPS limit on GD, along with turning down shader effects. Though haven’t been able to trigger a similar issue with my 3080Ti with settings all on max despite heavy SR34-35 testing and attempts to speed run SR30-31 with my own builds. Which I suck at lawl.
Mind you, I don’t give a flaming fluff about FPS drops etc, as long as they don’t get in the way of gameplay I can handle with ease stuff that others whinge mightly about.
Case in point, I only know about the DX to Vulkan trick because the Dead Space remaster turned into stutter city on me. Despite running flawlessly on my old AMD 590+ GPU when it came out. Finally found a solution after much fruitless searching, because google is crap these days, which was to use DXVK and lo, it fucking worked. Sure, I got some stutters, but it was otherwise un-noticeable to me. And even better once I got the 3080Ti, to the point you have to be uber autistic to notice them. Which I found out when I post a vid and promptly got whinged at lawl.
Lastly, word of advice, never trust any AI/LLM claims, because those systems are only based on the possibility of words coming after a word/set of words, not on context. Which is how they can fuck up 1+1=2 or tell you to put glue on pizza or in the case of Grok, spew total utter [redacted due to "no politics rule]. At least when Elon’s poisoned the training data and weightings, doesn’t last however.
Though I will say neural nets can do some useful things, but they’re going to remain limited until that field embraces the fact that neurons can do more than 1 function in brains, never mind the processing that occurs in axon branches. Aka biology already did the work on brains, just copy it already