Elliot,
Nick hit upon the other half of the signal. I had to go back to the beginning of your journey (2012-2013) posts to see the train room and the tables at the start.
All of the layout power and lighting wiring is in conduit. Did you do the same for all of the fluorescent ceiling fixtures?
If yes, you have 1/2 of signal circuit missing or blocked and using only the wiring in the walls.