Playing on Meph's Masterwork mod for 43.03 as an Orc fort, with the Meph tileset and TWBT enabled.
To start with, everything was going great and super speedy, 120 FPS or so (I think it's capped there). Fortress developed, I dug out more, got more orcs FPS gradually lowered, with occasional more extreme lagspikes that didn't last long. But even in the extreme lag spikes, while paused the FPS would shoot back up to 120 until unpaused.
At some point, with no obvious trigger, FPS collapsed to about 12 and stayed extremely low even when paused (would sometimes gain a few back, but never exceeding 20). It's not improved since, even hours later. For a while now it's been stuck anywhere between 8-15 FPS.
This happened when my population was at about 30, I think. There wasn't any obvious big engineering work to trigger it, although it might have overlapped with some of my workshop and stockpile space coming online. Currently my population is 53, animals ~40 (majority of them pastured or caged), and normally between 3 and 10 visitors/wild animals.
Damning the river and the waterfall made no significant difference to FPS (maybe increased it by two-three frames max). Designating large open spaces inside the fortress as low priority and creating normal and high priority highways across made no significant difference. Assigning 90% of the fortress to the military and stationing them in the hall made no difference. Shutting all the exits to the outside world made no difference. Sealing off the caverns made no difference. (I think) I have no doors that are pet impassable.
Does anyone have any idea what could be causing my lag here? I've got plenty of spare CPU and RAM capacity so I presume it's not my computer being over-stretched. Not sure what else to try other than maybe disabling temperature?
And is it normal for FPS to stay low even when the game's paused?