Report filed using feedback assistant - feedback number FB7783580. I've included some screenshots of the thread inspector, log output and attached a sample project.

Same problem here - I've tried using a playground inside one of my Swift package's dependencies and creating a Playground for my own Package - both compile fine, I can import my package module and auto-complete works ok but it crashes when it runs with a "Couldn't lookup symbols" error.

Also seeing this behaviour and sadly it's still present in Xcode 12 beta 4 (running on Catalina). Log output of the sample app I attached to my feedback report: https://gist.github.com/lukeredpath/0ba9ea748cf0ad90a64b5fa1dde4c3a1 Feedback number FB8116155 Please file a feedback using Feedback Assistant, maybe quoting the above number. The more reports the more likely this will get looked at. I haven't tried using an iOS 13 simulator as a workaround but note that this issue also seems to affect live previews in Xcode too.

Still a problem in beta 5, albeit with less verbose error output: 2020-08-20 17:19:39.345417+0100 Poker Clock[4805:114176] libMobileGestalt MobileGestaltCache.c:38: No persisted cache on this platform. 2020-08-20 17:19:39.503469+0100 Poker Clock[4805:113574] [plugin] AddInstanceForFactory: No factory registered for id <CFUUID 0x6000027cd3a0> F8BB1C28-BAE8-11D6-9C31-00039315CD46 2020-08-20 17:19:51.054637+0100 Poker Clock[4805:114341]&#9;HALC_ProxyIOContext::IOWorkLoop: the server failed to start, Error: 0x6E6F7065 2020-08-20 17:20:06.055809+0100 Poker Clock[4805:114182] [aqme] 182: timed out after 15.000s (0 0); suspension count=0 (IOSuspensions: ) 2020-08-20 17:20:06.056062+0100 Poker Clock[4805:114182] 244: CA_UISoundClientBase::StartPlaying: AddRunningClient failed (status = -66681). 2020-08-20 17:20:23.260456+0100 Poker Clock[4805:115401]&#9;HALC_ProxyIOContext::IOWorkLoop: the server failed to start, Error: 0x6E6F7065 2020-08-20 17:20:38.261055+0100 Poker Clock[4805:113574] [aqme] 182: timed out after 15.000s (0 0); suspension count=0 (IOSuspensions: )

Still a problem in beta 5. See feedback FB8116155

You need to create a personal access token yourself. Xcode used to do this for you when you logged in, but Github have removed basic auth from their API, so Xcode simply can't do that anymore.

I can confirm that this bug exists in Xcode 12.5/iOS 14 and also the latest beta of Xcode 13/iOS 15.

So initially, I didn't see any improvement in Xcode 12.5.1 - notably the iPhone 12 Pro simulator was still hanging for around 15 seconds before my app UI became responsive. However, erasing all contents and settings in that simulator seems to have restored performance to normal. I thought I'd tried this before so maybe something has improved.

For the record these additional keys are: NSAllowsArbitraryLoadsInWebContentUsageDescription NSATSExceptionUsage NSATSExceptionUsageUserChosenContent