Both versions: 1.9.1
Host: Ableton 9.7.7
Computer: Macbook Pro 2015
OS: High Sierra 10.13.6
Both are licensed.
When I load either the VST or the AU into Ableton, I hear the default patch just fine. But when I select another patch the audio stops, even after returning to the default patch. MIDI indicators light up, connection point indicators light up... just no sound.
Sorry you're having trouble. I can't say I've heard of this problem before. I still test in Live 9 and I have not run into anything similar.
Does it happen every time?
How are you changing the patch, with the menu / arrows on the plugin or something else?
I am having a similar problem with Virta, 1.9.1 in Reaper, on Mac Pro 2013, Sierra. When I am flipping through presets using the arrow eventually the plugin stops making sound. Visually it seems like everything is working. I am in the middle of a project so I can't take the time right now to trouble shoot it better but I will make a video of it in the next week.
I loaded up and tested again today... and of course neither Aalto nor Kaivo exhibited the behavior. As far as I know the only thing that's changed is that in the meantime I've quit and relaunched Ableton.
Please keep me posted. If it happens again, you can note if the output oscilloscope is still working. it shows the signal coming out of the plugin, so if there's any signal visible the problem is likely to be with the host somehow.
Re: Virta, some of the presets only work with audio input and some also work just with MIDI. You may know this, but it's the first thing I would check.