Primary problem: My corridor element is out in la-la land, translated 2,147,483.647 feet in both northing and easting. I have no idea where this originally came from; it wasn't a number I ever entered or translated the reference.
Using Geopak SS4 .872, I'm aware of the key-in CORRIDOR REATTACH. I tried it, but it didn't work. I believe now that it's because it's pulling the corridor baseline from the 3D element in the 3D model, seeing how it requires a profile.
This issue started when a coworker brought to my attention that my corridor was way to the northeast of what it should be.
I had recently converted all my files from international feet units (3048 meters per 10,000 feet) to survey units (39.37 inches per meter), which translates to a scaling factor of 1:0.999 998. In this case, the coordinates were all appropriate for survey feet already, so all I needed to do was change the working and storage units, which I did through a macro. In my view, this should have no impact on the scenario, but similar strangeness has only started to happen since this conversion. Though to be fair, it may have something to do with moving from .845 to .872.
So finally, I noticed in the Default model (2D), for a couple of my base files, the Offset X was equal to Offset Y but not equal to 0, which both should be. I changed them to 0. Now, in my Default 3D model, my alignment and another file still have the same non-zero offset. If I had to guess, there's already an article or thread on this issue, but I'm not really sure what to look for. Searching for offset yielded mostly stuff related to parallel offset elements. Searching for translation attachment didn't bring up anything I could use either.