If I plot the R-arm VDC drift times for trigger type 5, which is supposedly the LEFT arm singles trigger, I get the attached spectrum - very clean, low background, lots of statistics. This cannot be right unless trigger type 5 is not what it is advertised to be ...
Also, I only get a decent VDC time spectrum in the R-arm for trigger types 4 and 5. Isn't there a R-arm singles trigger? If there is, it doesn't seem to work.
On closer inspection of the time spectrum attached, it seems like there is double timing in trigger 5 on the R-arm as well: this time, there seems to be a secondary spectrum overlaid shifted by ~100 ns to the right (later times).
Please check the wiring of trigger 5 and the R-arm singles trigger.