I updated Xcode (11.4.1) this afternoon and noticed the new iPhone SE 2 simulator option. Cool! My iOS app was running fine on my physical device and all simulator before this update, but now when I launch the simulator, it freezes my MBP (2019 16", Catalina 10.15.4) while attempting to run. I can still move the mouse, but nothing else responds, and I'm forced to do a hard reset. Anyone else having this issue? Any suggestions on how to approach fixing this? I don't particularly want to keep trying it, only to repeatedly force reset my Mac.

  • File a bug report with Apple.
    – matt
    Commented Apr 29, 2020 at 3:49
  • Filed a bug report. This seems like a broader issue with Catalina than just the simulator - something with 'userspace watchdog timeout' panics. There's a pretty long thread of people with similar issues here. And there are a bunch of apple forum discussions as well. Still can't get simulator going.
    – cweber105
    Commented May 11, 2020 at 0:11
  • Thanks for filing it! This will help others. Even if it has been reported already, the more the better.
    – matt
    Commented May 11, 2020 at 0:19
  • Working through support calls w/ Apple. So far have tried all kinds of stuff: reinstalled Xcode twice, reinstalled MacOS (10.15.4), malware scans, system reports, system diagnostics, disk first aid, internet recovery. Issue persists. Next step is talking with an engineer in the next couple days.
    – cweber105
    Commented May 21, 2020 at 16:43
  • Thank you so much for reporting back! I'm going to suggest that this should be migrated to AskDifferent, as it is in no way a programming problem. It's about Catalina itself!
    – matt
    Commented May 21, 2020 at 16:51

1 Answer 1


Turned out this was a pretty fundamental hardware issue related to the graphics card with new 16" MBP. Not sure how many machines are affected, but it's easy enough to find threads and forums with owners discussing this issue. I met with a Mac technician at an Apple store and fortunately, she had seen the issue and immediately agreed to replace the machine. The new machine they gave me has also had a handful of kernel panics, but of a different sort, and they seem to have stopped suddenly after a few days of use. Keeping Apple on speed dial though if more issues arise.

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