Nice update. I'm just glad that things are moving along after a lull.
No migrants again.. It's getting a bit worrying. Those messages shouldn't be caused by the population cap, should they?
The time warping effect of the lake and the undead that have risen because of that are literally blocking us from outside help. There's probably a time bubble around our fortress now that steers migrants away; migrants try to enter on one side, but are sucked into a space-time anomaly and are deposited out on the other end without ever encountering the fortress. Don't ask me how invaders and traders are able to find their way here, probably some kind of loophole in space-time physics that excludes them from being blocked because they have prior site knowledge before the time warping occurred or some other nonsense of that kind.
But yeah, it's probably the site pop cap bug, namely there are probably over 3000 in the units list (total alive + total dead).
Did you manage to find the lever rooms? There is the one that controls the two above ground entrances in the main complex, then there is the other one in the south west tower that manages the well, magma cisterns and magma dike. Feel free to fill the magma dikes in, you can do it with dorfpower if you disdain messing with the reactors.
Also, if you have time, feel free to dismantle the pipeline
(and pump) that feed into the pool of lava to the southwest
(supposed to be a forge, but I didn't get round to finishing it. Oh well, we have yet another another forge now) You can dismantle the blue walls to the south of the pool on that side as well, they were supposed to act as drainage in case of magma overflow.
The pipeline is to the top right hand side of the picture (pump not pictured but on the same side) and the blue walls are self explanatory. You are welcome to finish up what I started and construct a forge over the lava pool by flooring over the relevant parts. Last of all, just a heads up, but make sure you have trade goods for autumn, I made a huge order last year.