Xcode 12 can't debug

When I try to debug with Xcode 12.0.1, when it hits a break point, it will typically give me a progress indicator forever in the variables view and debugging is hung app (Xcode itself remains responsive). There's been a number of reports like this with older versions and I've tried everything suggested (reboot machine, delete ~/Library/Developer, delete Derived Data and reinstalled Xcode. Nothing has worked.

I rolled back to Xcode 11.7 and it's working fine. This is on an iMac 2020 with 10 cores and 72GB of ram. It appears to work fine on my 2019 MacBook Pro, however. iMac is running latest Catalina and MacBook Pro is on latest Big Sur beta.

Is Xcode 12 just not ready for prime time or is there something I can do to resolve this?

Thanks for any help!
//Ray