Those must be an event when a window pane on the floor above the place where the sensor resides cracked and fell and sliced the cable leading to detector. Took some time to fix things, probably just reallocated sensor ID to another station nearby. Old story.
A fun experiment in metro area would be not just measuring background, but actively filter air and measure what's left on filter. I too have a gamma scintillator crystal setup waiting on a shelf for a day when I have enough time to return to using it.
Didn't Finnish IQM do it already?