I've been having a problem along these lines with Cab Lab 4 on FM9 fw v6 beta 1. I'm on a mac pro running OS 10.14.6.
I've been following Cooper Carter's tutorial for Cab Lab 4 and when I get to the part where I select SW Live Mode in the Audition section of CL4, I lose audio when I select step 3 (Disable Cab Processing in my Preset). I tried the fix listed above without any success so far. I'm using the FM9 as both in & out for monitoring purposes. When I click the test button I get the correct tone through the selected audio output device per the Audio MIDI settings. I've tried this with both FM9 and my Universal Audio audio interface. They both work correctly whenever I select them as the output device, but as soon as I select SW Live Mode I'm not getting any audio out of anything.
I've also tried manually disabling the Cab block from the front panel of the FM9. I'm still not getting any audio when I go to SW Live Mode. Prior to going to SW Live Mode I can hear that the Cab block is already off, but I'm not hearing the selected dynacab.
When I checked the privacy & security settings on my mac, it shows the microphone already has access in Cab Lab 4. I also tried giving Cab Lab 4 Full Disk Access - no change there either.
The other thread that discusses issues with using the SPDIF out didn't really offer anything that led to a fix in my situation. I did try connecting the FM9 audio out to my audio interface and selecting it (UA Apollo Twin) as both the in & out device. Rather than the FM9. I still lost audio when I selected SW Live Mode. When I tried HW Manual I could hear the preset with it's cab block muted, but when I'd click send to send my edits in order to hear them, it would behave as if it was trying to send something, but if it worked, I still couldn't hear it. Whatever audio is supposed to be coming back via Cab Lab 4 isn't making it out of either audio interface so far.
I'm not sure what I might be doing wrong at this point. I haven't filed a support ticket as yet. I was searching the forums first in hopes of finding a solution. I'm not sure what to try next aside from opening a support ticket. Any suggestions? Thanks!