I Need Help
 

Hello friends. I was able to view my friend's find my position a few weeks ago, but last week, even with his location settings and mobile data settings turned on, I couldn't see his location unless he opened the app, at which point I could see it, but after he closed his app, I couldn't find him. On my end, the states would say "no location found," but on his, he could see mine very clearly even if I had closed my app. Please help me.

Sounds like he needs to adjust the permissions of his app

On your friend's phone, go to settings, privacy, location services, find my and check what is checked under 'allow location access'. It should be the third option 'while using the app'. Go back one level, go to 'Share My Location' at the top of the menu and check that you are listed under 'Friends' and 'Share my location' is switched on. To be sure, switch off his phone and switch it back on. After that, if it doesn't work as advertised, contact Apple and ask them what to do.
All of the above is based on the two of you using an iPhone, if it is a different brand, you'll need another helpful person.

If he has recently installed the app on an additional device, perhaps this is the problem. My wife was convinced I’d recently deliberately switched off my location because her iPhone couldn’t find me when I was away from home. She was actually seeing the location of my iPad in the house, which also had the app. I’ve uninstalled it from there and now she can keep tags on me.

Didn't Apple recently change their method of allowing stalking apps (that is what they are, don't beat around the bush) to access vital information needed to send to the stalkers? Maybe a phone upgrade has defeated your apps functionality?

Privacy is like virginity - once you lose it, it is gone forever...

The 'Find My' app is from Apple itself, I wouldn't expect a phone upgrade to have significantly changed its behaviour.