Were there eggs in the pit, or did they just dig the pit and just abandon it? You will definitely know if there were eggs in it, the bolivians are pretty protective, and will push away any intruder. Could be that they just weren't quite ready yet, and just abandoned the pit. One thing I noticed is that they prefer laying eggs on a smooth flat surface, so if you had a small piece of granite or something flat and smooth, and bury it where the pit was and just leave a little exposed, they will uncover it and spawn there. Almost guaranteed. That's what they did in my 75G, on granite, then when I moved them to the 29G, I took another piece of granite and did the same thing. Within a day, they found it and had it completely cleaned off, ready for spawning.
And another thing I noticed in my tanks, once they spawn in one spot, they will continue to spawn there. Won't move locations. The only time they change locations is after the eggs hatch and you have wigglers, they will dig several new pits and keep moving them around to throw off any enemies that might have noticed them. Mine usually would move them in the evenings.