I've had this issue a few times recently, and googling for troubleshooting info seems to come up empty. I'm running Amplitube 4 on Mac OS 10.15 with my iRig Stomp IO. When I go to use it, I plug in my bass into my iRig Stomp, plug the iRig Stomp into my MacBook Pro, and the Stomp is clearly getting power as well as signal from the bass, as the gain indicator lights up on the Stomp when I play. But nothing happens in Amplitube - no sound, no gain indicators, no movement on the tuner, nothing.
I have iRig Stomp IO set as the input device in Audio/MIDI setup and my MBP Speakers set as the output. All other settings in Amplitube itself are the defaults (except I'm trying to use one of the bass presets, since it's a bass, after all).
What could be preventing the signal from making it to Amplitube?