Thanks for the quick response. This is a local single player world. When the crash initially happened I could load back up for a few seconds but I didn't manage to get a screenshot as I just thought it was another random crash. Everything looked mostly normal, I managed to switch a lever which should turn off the computer, and thus stop the machine from moving, so the frame is definitely not moving any more (indicated by blue light on motor).
The one thing I did notice, was that the conduits (which seem to be causing the error), weren't connecting to each-other, or to the mining wells. They all were rendered as disconnected single conduits. Realizing this I did try to quickly remove a few of them after turning off the motor, but didn't manage to get them all, and now the game instantly crashes when I load up the world.
As for the heavy load, again it's just on my local machine, which is pretty capable. I was starting to wonder if somehow the mined blocks had begun spilling into the world on the other end of the item tesseracts, but haven't been able to check. Is there any indication of this in the error? Regardless I don't think I had the machine running for long enough to cause this much performance hit on my machine, even if the items were spilling errr'where.