HALion 7 weird cpu dropouts

Hi all

Experienced a weird problem today after loading H7 into a project to build a very quick custom synth. I was using analogue mode with just two oscillators, no lfos, no fx, no automation, monophonic. I just needed a very quick square-wavey bleep, to create a one bar little run of notes.

I almost immediately started getting frequent cpu drop outs. But the cpu reading within Halion was basically 0% (as one would expect with something this basic).

Rendering in place took very long - 1 bar maybe 15 to 20 seconds to bounce. No simultaneous vsts playing back. After rendering my little sample out, i removed the Halion track and the dropouts stopped. Any idea why this might happen?

Cubase 13 Pro. MBP M1 Max, 64gb ram, 32core. Sonoma.

Cheers