I added analytics and sent out a TestFlight build. I was able to catch FileManager .contentsOfDirectory call taking upwards of 20 to 400 seconds when reading the files in our custom image cache directory in the aforementioned app group storage. If the cache was unable to clear itself out, I supposed the number of files in that directory could grow. Would the .enumerator(at:URL allow me to access that without blocking other disc access? It's possible this call itself is being blocked?

I can't say everything here, only allowed 500 characters. Some of the data I observed not initially loading but loading after 2 minutes is in #1. It's a core data store in a subdirs of containerURL(forSecurityApplicationGroupIdentifier: used to share this on-flash data with a PN service extension (which only ever reads core data, and never saves). Using a FRC, we don't know if it's saying there is nothing in the core data store or if frc.sections?.first just returns nil after performFetch.