Ok, I think I have cracked it.
So I was doing research on what (null) is and found another Apple support communities thread that was from someone who had had the same issue except with an app. And it turns out that the app hadn’t downloaded/synced properly with the phone so they reinstall and the app and it worked fine. And most of you are saying that you can’t open photos after seeing the message, so my thinking is that it is something to do with the photos app so my thinking is that if someone who had seen the message were to reinstall from the latest iCloud backup or maybe restart the device and that might help. I haven’t seen the message since restarting my iPad so I though it might work on other devices? Let me know if it works.
Cheers.
Link To Article:
Iphone hacked? Null app in settings - Apple Community