Hi,
I have a similar issue, I am also loosing sound in the right channel frequently, the problem can be "fixed" by turning the volume quickly high up, and then down again on the AMP, and the sound will come back into the right channel (but the problem will come back again), my first guess was the AMP was broken, but I have the exact some issue when connecting another AMP.
I have tried to connect the WiiM Pro with ethernet and WIFI, and also connecting the audio with all of the options (SPDIF/RCA/COAX) but this hasn't solved the issue.
I am using an iPhone with the WiiM Home app to operate the device.
I really hope a firmware fix can be provided to fix the issue, the issue is driving me insane, and I really don't want to replace the WiiM device with another streaming device.