I haven't measure how long it takes to happen, but it tends to be 'after a while'. This is the first time I've realised it stops after several more hours, which was a surprise. I'm trying to measure how long it takes now.
Is there a way to figure out what's getting processed when this happens?
I'm currently running the process with both of QJackCtl's d-bus boxes unticked to see if (and when) it happens again. PulseAudio isn't installed and I didn't have my ALSA bridge running when recording the video, but I won't start it today anyway just in case it would make a difference. No process spike yet...