annoying problem with Douk Audio U2 Mini and SMSL PO100 Pro

[morethinkingcapacityneede]

Currently experiencing an annoying problem where the USB-SPDIF bridge I am using does not work properly if only R channel is transmitting from the computer. My understanding is that the clock for the output is derived from the L channel, so when doing a sweep with R only, the PLL unlocks halfway through the measurement. I see this behaviour with Douk Audio U2 Mini and SMSL PO100 Pro USB->SPDIF interfaces.

Has anyone seen (and overcome?) this issue before?

My next step is to try using a Topping D10B as an USB bridge.