Strange Behavior: 1746 OW16 (Allen Bradley SLC500 Module)

I have two output cards sitting next to each other in a rack:
1746-OW16
1746-OW16 (Octal)

output 13 in the first card triggers a solenoid. When output 15 (17 octal) on the 2nd card goes high, the output on the first card drops to zero volts.

When output 15 is low, output 13 works fairly well. The voltage looks normal (120VAC) most of the time, but sometimes still drops to 0.4VAC; however, when output 15 goes high, output 13 drops within a few cycles.

I found a spare output, and used that, but I'm not sure if I should just replace the card, or if there may be some underlying issue that I'm not seeing. It may also be a red herring,

Maybe it doesn't have anything to do with the card. Maybe there is something wrong with the wiring of the solenoids? Issue with the common wires or grounding? I would disconnect all wires from the outputs of the cards, force each output on from the PLC logic, then measure each output with a meter. (With nothing/no wires connected to the outputs.) This will help eliminate if it's a bad card or if it's caused by the solenoid wiring.

I would look at the logic first to see if you can figure out what is trying to be done.

then look at the wiring on each card.

james