Changed rigs from KX3 using serial USB adapter to K3s with USB radio interface. Before WSJTX worked fine but suddenly the FT8 mode would randomly just switch from audio signal going to K3s via usb to monitor the audio on my Mac 27 inch thunderbolt monitor. Checked for potential timing problems, varied delay, reconfigured audio on the Mac several times and it kept happening on the K3s usb audio but worked fine with KX3. Started checking diagnostic info from WSJTX. Realized it was the program misbehaving latching onto other audio process when the K3s was running though the monitor port on the display monitor. I moved the usb cable to the back port on my Mac Mini and the problem stopped. Apparently the usb bridge in the monitor was introducing enough random delay the program would logically switch to the monitor audio stream depending on what other background tasks the Mac was doing. I know the priority of the USB ports on the Mac motherboard is higher than external bridge and external monitor bridge ports from some work I did several years ago with some USB drivers. I believe this is similar problem depending on the usb hierarchy and how your computer is put together. Probably adding an unique interface names and a timer to let the Wsjtx program hang onto established usb streams longer so as to have them not switch around for lowest latency path would be cool. Just a thought but what do I know ? I am just surmising :-)