Slutter usually associates with spikes in GPU & CPU usages. I assume you have your OS on the 120GB SSD and your game on the 1TB HDD? Anti-virus or similar programs could create interruptions which explains the drop in usages. May worth looking into.
Could be RTX related issue. I made an upgrade from 1070 to 2080 and I also noticed slutters. I have the 8700K, so I'm sure it's not cpu bound.
Are you monitoring your CPU, GPU, and memory in games? Did you see any spikes in usages?
Happened to my company 2 months ago. We didn't pay the ransom of course. Took us more than a month to completely recovered. Absolutely a nightmare. Luckily, we'd transited to a cloud-based ERP system last year. Otherwise, it would have been even worse...