Weil-McClain GV series 4 circulator voltage

[AKJM]

While checking some other issues on a Weil-McClain GV-6 series 4 boiler, I noticed the 1013-200 control module was outputting 120V to the main circulator and only 90V to the bypass circulator. The boiler manual specifies 120V at both output terminals. I had access to another control module which tested out the same: 120 vs 90V. Is it normal for the voltage to the bypass circulator to be lower? If not, what could possibly be causing this? Thanks