On the RPi 3 using USB audio and Ethernet (which is an
internal USB
device) together was near impossible. Does the RPi 4 still have this
problem ?
It's been a while but it had something to do with USB and ethernet being
shared on the same bus like Bengt already pointed out, see also
https://wiki.linuxaudio.org/wiki/raspberrypi#usb_audio. On the Rpi4
those are separated now so I guess ethernet interfering with USB is not
an issue anymore.
Best,
Jeremy