I encountered the same issue, but it only happened on our iOS 12.1 device. I did a few Test Flight builds last week, which work fine, then did a couple this week that fail to launch on the iOS 12.1 device. It works fine on our other test devices. Very little changed between the builds and Ad Hoc builds work fine. I suspect it had something to do with bitcode processing, but I never really go to the bottom of the issue. I updated that test device to 12.5.6 and the problem went away. I figure if our real users encounter this, it'll be a pretty small subset and they can upgrade their OS to resolve it.