Thank you all for your ideas, I managed to solve the problem. It was somewhat hardware related, but not really.

I was using BTRFS, which creates a lot of write amplification and aged SSDs don't handle that well. According to a study from 2017, btrfs can cause up to 32x write amplification, absolutely hammering its performance: https://ar5iv.labs.arxiv.org/html/1707.08514

I converted my system to RAID0 using EXT4 and the stutters and freezes are gone.

Try searching it on https://btdig.com/, a DHT search engine. Most of the torrents there are very old and have barely any seeds. Be patient. The last thing I downloaded from there took 1-2 weeks to complete.

That's what I do. I seed for as long as it remains on disk.