Actually, the problem seems to extend to launching the Simulator app also. Sometimes just launching one of the iOS devices in simulator will freeze the entire machine, and other times it works okay.

Thanks so much for your response! I upgraded to Xcode 11.6 this morning and now when trying to get a freeze, I'm not getting one, even when I stop doing my workarounds to minimize the problem (I found disabling "Parallelize Build", never using the Previews, setting the Simulator to prefer the Integrated GPU, and always opening the Simulator before Xcode helped). Maybe there was a fix in Xcode 11.6? In case it does start freezing again - one question: if I run sudo spindump 100 -o ~/spindump.txt first, I get an error message: perdue@mac-135246 ~ % sudo spindump 100 -o ~/spindump.txt Cannot find process with pid or partial name 100 I can run "Spindump" from Activity Monitor, but when the system freezes, I can't access Activity Monitor. How do I get a "pre-emptive" spindump? Thanks again!

For what it's worth, the problem has resurfaced, but it does seem to be tied to what else the machine is doing, and it is still sort of random. So I'm not quite sure how to get a pre-emptive spin dump... Thanks!

Just to close this off, the problem went away after one of the OS point upgrades. I had built a workflow that carefully went around this, so I'm not sure when it happened.

FWIW I finally got an answer on Stackoverflow with some promise. orj says: You could populate a test database on a device then dump the application data container (see https://www.codementor.io/@paulzabelin/xcode-app-data-suni6p4ma for a tutorial) and use that container in your UI tests. This looks like a pretty good idea.

Thanks a lot for the replies and thoughts. Do people have favorite resources for learning the ropes as a small business? I've been reading "Small Time Operator."