External audio source stopped working using iphone

I have been streaming Facebook live for 9 months now using external audio via usb from my mixer to my iPhone 8 via a usb/power lightning adapter. Suddenly this week it has stopped detecting the audio. I have experimented with starting live first and then connecting the adapter but no joy, also many other options . All cables and the connector are fine as it works on my iPad. Anyone know what I can do?