Xruns when using sustain with superdirt synths

I had a lot heavy cracking and clicking when playing and recording a couple of experiments. Jack had a lot of xruns and I set out to deal with those -- closing every other program, increasing jack and/or tidal latency, but still many xruns.

And after a good amount of trial and error, eventually those xruns disappeared when I disabled the sustain parameter on the synths I was using; I confirmed this happened with superfm and superpiano, where introducing a sustain effect would bring up many xruns.

Now, I still get occasional xruns when taxing the CPU with heavy desktop switching, but it's sustain that seems to make my CPU push beyond what seems reasonable. Is this expected behavior? Maybe I'm missing something obvious?

This isn't expected behaviour.. Definitely worth reporting as an issue, with a simple example that causes the problem if possible. https://github.com/musikinformatik/superdirt/issues