I disabled parallelization and it can "work"—I mean, Xcode can launch the test runner app, but one instance will still get stuck and consume up to 70–80 GB of memory. Finally, I found that when this issue occurs, the Xcode console outputs something like "Interface orientation changed to Portrait" and then gets stuck. So, I tried unchecking all other orientations except Portrait, and it finally worked. I spent two days on this issue and hope that my findings can help someone who is still struggling with it. For someone who needs to enable all orientations for their apps, I would suggest checking your code that may be triggered when the device orientation changes. I believe this might be the root cause.