Rdr2 (and other CPU-intensive games) on nvidia eGPU  

Just updated my eGPU setup from 1080 to a rtx 3080 and... Was blown away at how Doom eternal runs at 4k with close to max settings (on nightmare) at 120fps!!!

But, then, I tried RDR 2. Aaand... I cannot understand. In some places it runs ok (e.g. facing water, fields, even in forest), although counter shows just 30-45, it feels smooth and fine. But when approaching the main camp (or other places like that: people sitting around a fire, or a stagecoach in the dark, a train..haven't played much to make a full definite list), fps drops to 7-12 and sound  is stuttering, game goes in full meltdown!!

Monitored the cpu, in doom it is below 40% load, rdr2 - around 50, sometimes 65-75%. There is no clear spike when the "meltdown" happens, it could be around 60% load and running ok, then it stutters completely(like, literally unplayable 7fps and torn sound) for 10-15 sec and CPU is still around that 60-65%. 

Tried at lowest possible rdr2 graphics settings, really doesn't help at all in these stuttering moments (e.g. when I approach the chapter 3 camp).

I am interested in what is the cause of this, maybe someone encountered something like that also? Seems like a very particular problem with some element of the game, not a general eGPU/CPU bottleneck, I mean...totally lowering the graphics doesn't affect this at all, even at very low res :O.. although CPU does run a bit high for this game. I am sure I am running on the 3080 eGPU and not iGPU or the amd 5500M dGPU.

Setup is: MBP 2019 16" base, Razer Core X Chroma, nVidia rtx 3080 + external monitor.