Zhihong had analyzed data from the right arm and found some problems. Upon checking the left arm, it was discovered that the twisted pairs taking the ADC gate signal to the ADC modules were connected incorrectly (my fault). They have been connected properly.
Additionally, twisted pair 10 had become unplugged from its ADC module and was plugged back in.
After that, everything seems to be working.
Also, the pulser signal constituting T8 from the right arm was connected to a cable sending the signal to the left arm, where it is set up at T8 on that side.