TL;DR Laptop keeps switching between Signal Link audio output and speakers. Problem goes away when I turn TX knob down far enough on Signal Link.
I just bought a SignalLink and have it connected between my laptop and my radio (a Yaesu FT-450D). I've successfully made a couple QSO's on FT8, but keep running in to a problem.
When I tune the tx knob too high, the computer seems to change the audio output from the Signal Link back to the speakers on the laptop. As a result, the Signal Link doesn't get an audio signal any more and it turns off the PTT. After a moment (well less than a second), audio switches back to the Signal Link.
I can avoid the problem by keeping the TX knob turned way down, but them my actual transmitted power is way lower than intended.
Details: Radio: Yaesu FT-450D Laptop: old Dell running Ubuntu 18.04