fastcat95,
Perhaps "picky" is not the best word. The user manual states to try non-audiophile cables, free of adapters, that meet the USB 2.0 specs. I can't say what all that means as the USB 2.0 spec is 650 pages long. However, the spec indicates a 4 wire connection and shield. Contact 1 is VBUS - the power. I think that some audiophile cables may not use the VBUS. So, I take the Urd user manual to say the cable requires all the connections.
I think the connection issues for some folks may have been where people have been using whatever cable they had lying around, and/or using adapters. On SuperBest Audio Friends I see one fellow has been using an $8 Amazon cable successfully.
Another potential issue here is you state that you are using a Denafrips Pontus DAC. The Urd user manual states the DAC must be UAC2 compliant. Denafrips specs for your unit state use of a "Proprietary USB Audio Solution via STM32F446 Advanced AMR Based MCU." It appears Denafrips wrote their own USB controller code. Is their controller UAC2 compliant? Are you using their latest driver?
The final issue is that you say the Potus USB requires 5 V to trigger the reciever. Does the Urd supply that? That's a question I would ask Schiit. I know they did extensive compatibility testing over an extended period of time. Did you ask them if the Urd had been tested with your DAC?
On the Urd, do you get the broken USB icon on the Urd or an exclamation point?