We started a run and it was working fine but the 2D images on the screen from the detector had no signal in them.
Checked all shutters were open and they were so very confused.
@Dan Olds figured out very quickly the problem (Thanks Dan)
We had restarted the bsui environment. This resets the state of the experiment back to where it was right before the restart (nice) EXCEPT that by default it resets the detector back to the default detector and not the detector that was being used before the reset. In our case the default detector was the far detector (which we weren't using) and so the simple fix was to set the experiment detector back to our active detector (pe2).