After creating my first subsurface entry, my performance dropped drastically, with stutters happening.

Of the 16-18ms/tick update times, Subsurface appears to take 6-8.

Edit: Might be a duplicate of https://mods.factorio.com/mod/Subsurface/discussion/6869df7fe53b471a55afb877 as the issue only happens when the miner I was using was causing pollution. I'll try other pollution making techniques.

Edit 2: Small burner generator doesn't cause this issue, nor does the hauler. My deduction is that it's something specifically related to a special interaction with the Miner vehicle. I'll try KingJo's bulldozer.

Did you ever figure out a solution? I seem to recall that the KJ Bulldozer doesn't work on subsurface's walls, and I had the same problem as you with the miner vehicle.

Nope, and eventually something made the subsurface run terribly, so I just gave up on it for now