A fundamental characteristic of USB interfaces and Bluetooth is that both ends have to electronically recognise the other end and agree to talk to each other before proceeding with data interchange.
The various standards and protocols for these interfaces are updated every now and then, and it seems quite common for problems to arise, frequently when the phone software is updated...
Have you followed the suggestions at the following apple support web site ?
I only use mine via Bluetooth and I know that frequently when streaming via Amazon Music that nothing will come out of the speakers despite it being connected and the play bar on the phone moving along, and also the current song showing up in the Cactus display. I can FFWD & REV tracks on the phone and on the console and it'll change tracks but nothing plays.
Its at that point I say "$%&k it" and listen to the radio.
I just bought a new Cactus and also am having issues with streaming Spotify. The phone pairs ok, I switch source to Bluetooth , the song I'm playing in spotify appears but not sound comes out. Has anyone found out a solution for this?