I ran into the exact same issue: I have an app that uses ExportSession to resize videos and livephoto videos. This can run both in foreground or background, and I usually process at most 4 assets at a time. This works 99% of the time, but randomly it would get stuck waiting on exportSession all at the same time. I would wait indefinitely without any error. I tried to kill the app in task switcher or restart from debugger but nothing works short of rebooting the phone. I do not have diagnostics because this issue is very rare and happens randomly. I do observe it happen more often on my iPhone11 than on iphone6 https://feedbackassistant.apple.com/feedback/9188280