Hi Cormac D -
I can't reproduce that here—adding or editing channel strips works reliably (MainStage 3.4.2, Mojave 10.14). Catalina is well-known to still have problems with audio software & plug-ins, even Apple software (like MS, GB, & Logic), and I did find several reports of people having the same issue with MainStage 3.4.3 on Catalina, so it may be a bug related to either that MS version or Catalina (or the combination). At least one user reports that reverting to MainStage 3.4.2 stopped the crashes, so if that applies in your case, it might be worth a try; another says the issue doesn't occur with a new/plain Concert, so that would also be worth a try..
It sounds like the above scenario might be a likely culprit, but you could also try any of these standard troubleshooting steps below:
- Hard shutdown & restart
- Turn off WiFi while running MS.
- Delete MS Preferences (save them on the desktop as a BU if desired)
- Temporary disable AU plugins (though if the crashing is related to a specific action, that's a less likely factor).
- Try the same behavior that triggers the crash in different MS files/Concerts
- Try the same behavior that triggers the crash in a new (relatively) blank Concert (like Keyboard Minimalist)
- Try the same behavior that triggers the crash running MainStage under a new (test) User
- Revert to an older version of MainStage (as suggested above)
- If running a older version of MS, update it (but always save the current version as a renamed .zip file, just in case)
- If possible, try the same behavior that triggers the crash while booted into an older macOS version [pre-Catalina]