The ARKit lifecycle [ https://developer.apple.com/documentation/arkit/managing_session_lifecycle_and_tracking_quality ] doesn't include killing ARKit outright. Best to revisit your expectations about shutting it down completely yourself and work with the API as designed, I think.
My opinion is that what you're seeing is expected behavior and yes, the system should kill as needed. Suggest you file a bug and see what comes back, being sure to add your report # to your thread for reference, thanks and good luck.
Okay, thank you. I'll go ahead and submit a report.
EDIT: Report Number: 46451526