diagnosticd is a daemon you need to stop/kill with launchctl. The daemon you most likely need to stop has 'SimDevice' in its name. To get the exact name do:

    /bin/launchctl list | grep SimDevice

Then with the appropriate name(s) (there could be more than 1) do:

    /bin/launchctl stop 'name'

In my case 'name' was: `com.apple.CoreSimulator.SimDevice.380EFF06-B636-49CD-851E-5DB4890641AE`

Oh, and dont forget to file a bug report with apple here: https://bugreport.apple.com/web/

Btw, its kinda fun to see playground/diagnosticd struggle with your code; if you create a bug or some other elaborate syntax, cpu goes up. If you clear it, cpu goes down (just a bit). Almost hilarious how Apple implemented this...