Also experiencing this issue - reported at Unreal Engine Issues and Bug Tracker (UE-156807)
I’m suspecting the issue is the UDP plugin as it says when you hover over it “Note - in Shipping builds ALLOW_UDP_MESSAGING_SHIPPING=1 must also be defined in TargetRules for messaging to be available with or without this setting”
Investigating on how to add this flag and will update if it works
Continuing the discussion from iOS AR app shows black background rather than a camera overlay in production: