Screeching when record arming a midi track

I’m running Cubase 8.5 on OSX, triggering VEPRO on a PC. Occasionally, (like every few days) when I record arm a track, the audio engine goes haywire and produces an ear shattering screech, pinning the meters…almost like the dreadful midi feedback loop I remember from the early days of DP. When I disarm the track, it stops, but starts again whenever I arm the track (or another vepro track) again. No settings have changed from 1 minute prior when I so freely could select a track to record without punishment.

Looking at Vepro on the pc, I can mouse-click on the on screen keyboard and produce notes that appear fine in kontakt meters. But when I come back to Cubase on the mac and select a track to record, screech again.

I went to the devices menu and re-selected my device and hit apply and that seemed to temporarily fix it. I can’t remember if audio tracks have the same issue. But the problem is not present on Logic Pro X.