It's a startup timing/sequencing issue. The USB device hasn't initialised and loaded drivers before Kodi starts. Kodi evaluates the available audio devices once at startup and nothing is present; hence the device "disappears" and reverts to some other default. If the device has loaded drivers before Kodi is started the device is visible and can be selected.
You can solve the problem by setting the badly named "wait for network" startup delay in LE settings. A small delay should give the drivers time to load before Kodi starts. Something like 5 seconds should do the trick if it's borderline.
I'll try this, thank you.