1769-of8c tie to 24vdc- for common signal

We have belimo valve that is getting powered by 24VDC power supply. That same power supply is feeding the DC+/- of a OF8C analog output module. Right now, I have a 500ohm resistor across the 4-20MA output to generate 2-10V. The issue is that if I measure the AO+ to 24vdc-, I get 34VDC. If I try and tie the AO- directly to 24VDC-, I fault the power supply... What am I missing here?

The PLC power supply is seperate from the 24VDC power supply powering OF8C and the belimo valve.

https://forum.automationdirect.com/forum/general-applications/111253-converting-4-20ma-output-to-2-10-vdc

The above thread may help you out. They are also using a belimo valve.
Regards,

Follow up. It looks like they have some serious miss-wiring either in their panel or out in the field devices. I started pulling off field wiring and was able to find a few of the cables that were backfeeding voltage. Hopefully the high voltage on the valves did not damage them, but they were not able to get them to move.