I figured out my problem. I had configured the app extension with a different prefix from the main app. The main app has my Team ID as the prefix. Somehow I configured the extension to have some other prefix for its bundle identifier. I fixed it by creating a new App ID for the extension. Thank you for the reply, Quinn. John

After I was still seeing the behavior when just creating an App Delegate, Scene Delegate, and View Controller that did just about nothing else, I deleted all other code in the app. I could then see the problem was gone. I then put a breakpoint in every method with a dispatch_once_t call. That led me to where my code was being called that I did not expect. I hope this is somehow helpful, @SeanMcMains! John

The crash report said the reason was running out of memory. The app's memory usage would climb by roughly 30MB/second until the app crashed. I since figured out the source of the problem. I had an Objective-C extension on UIColor that implemented secondaryLabelColor. I do not know why that had the effect it did on share sheets, but removing that extension method fixed it. Thank you for replying! John