As per #p29861
Using the current release (ending 18?) at the time of writing, on an RPI3, it only has a wlan0 with onboard Wifi while AP is enabled. When you disable AP, the interface is removed, and you can’t enable Wifi properly. A USB stick worked as expected.
While AP is enabled, via onboard Wifi, it doesn’t see all SSIDs, and can’t successfully join any (possibly some on CH4, but that’s too crowded to use here).
So there seems to be a pair of problems- in the initialsation of the interface at all without AP, and then possibly with the drivers too. As a sanity check, on the same Pi3, Rune Audio works just fine with the onboard Wifi, and connects to my normal AP (which tends to be on CH13).
I tested with a freshly flashed card, and it still happened- so it should be trivial to reproduce. If it refuses to break for you, feel free to give me a poke