I can't remember what the timeout value is, but say the A12 puts some users on the limit, say due to library size. That could be the issue. (I'm sorry, I haven

I can't remember what the timeout value is, but say the A12 puts some users on the limit, say due to library size. That could be the issue. (I'm sorry, I haven't dowloaded the app so I'm guessing on your UI, just know its a fairly common mistake) If you're just putting up a dialog saying "building index", running the code to build the index in the same thread, then dismissing once done, it will lock out UI updates, eventually leading to a crash (I think it's 30 secs for the timeout). Running code in a high priority background thread with a callback to the main thread is fairly trivial in iOS, there's the fine grained control of GCD, Combine for react like code, and the new async/await pattern. A UIActivityIndicator can be used to show activity without knowing progress.