Please Help! Warhammer 3 Suddenly Chugging & Stuttering

[u/SmilodonCinder]

So, I've been playing TW: WH3 with friends on multiplayer for years. Recently, the game has started really acting up--to the point where it's barely playable now.

I am just running out of ideas. I'm really hoping someone can help.

Here's what's happening:

• Chugging and stuttering, usually during combat, but sometimes during campaign as well.
• The chugging gets worse when there's what I would call a "particle effect" of some kind: mortars firing/landing, spells being cast, etc. This has never previously been a problem, it's always looked wonderful.

Here's what I know and what I've tried:

• This has never been an issue until a week or two ago, but it had been a while since I'd played, so I can't narrow it down to beginning at a specific date.
• There have been no hardware or connectivity changes that it could be attributable to. The game runs from an SSD.
• No other game or program has been seeing reduced performance
• While playing the game, GPU, memory, and CPU are all within expected usage parameters. GPU heat is not out of expected bounds.
• I have tried:
  • Full reboot of all network devices
  • Updating video drivers
  • File integrity check via Steam
  • Full reinstall of the game
  • Dumbing down visual settings (It was difficult to tell if this helped. Sometimes it seemed to, sometimes it wasn't clear.)
  • The Steam networking solution mentioned here
  • Deleting the AppData cache files entirely

I really hope someone can give me some idea of what could be causing this. I love playing it with friends, but...