qBittorrent using 100% disk and speed fluctuates wildly

[tsmswifty]

When I try to download with qBT the speed starts fluctuating wildly and disk usage quickly reaches 100%. This hasn't happened to me before; not sure why this is. Is there any way I can get torrents to write sequentially to disk rather than in random chunks? My disk is new (ST2000LX001).

Settings:

Disk cache is on 0
Enable OS cache is checked
Guided read cache is checked
Coalesce read/writes is checked

[Switeck]

Looks very similar to these speed issues:
https://github.com/qbittorrent/qBittorrent/issues/7954
https://github.com/qbittorrent/qBittorrent/issues/8284
https://github.com/qbittorrent/qBittorrent/issues/8780

Is qBitTorrent's Disk Cache set to disable (forcing HDDs to do more work) or auto-manage?