To reproduce:
-Create empty Unity project, create empty scene, attach the example script to gameobject and run on iOS device.
-Tap on "Safely request time" and wait until app loggs "Done" to console
-Press "Power" button on device
-Unlock device and resume app
-Tap on "Safely request time" and wait until app loggs "Done" to console

Result: udp request will be repeated successfully

Now restart the app and repeat all steps with "Unsafely request time" button

Result: app will crash on second network request