iOS Wi-Fi is turned off for some application and cannot turn on?
2ND UPDATE:
It got worse after iOS 14.2 update. \WLAN and Data for Camera and some critical apps are turned off so I had to do extensive search, or the phone would become somewhat unusable.
Cause: The cause seems to be the Watch app. There are some connections between apps on the Apple Watch and iOS, and there seem to be a bug regarding how the network setting are shared and sync'ed between Watch and iOS apps. So most likely the problematic apps had been installed both on iOS and Watch.
Solution: Reset all settings. Resetting network settings wouldn't work. You have to reset all settings (no data or media would be deleted).
Go to: General &gt; Reset &gt; Reset All Settings. After a reset you are done.
All settings will be deleted, so you will need to do some configurations. Wallpapers, dark mode, keyboard, region, date and time, Siri, etc. However you get to keep all your apps and data, which is okay to me.
Don't forget to turn on Siri as you lose CarPlay capability if Siri is off.
======
UPDATE:
Again this problem is gone with iOS 14.1 update that was applied two days ago! Apple please look after your regression test.
======
Sadly, this problem is still there even in latest iOS 14!
WLAN and Cellular Data will turn off for random apps and could never be turned on. Last time I saw this was on my iPhone SE 1st generation with iOS 12.
There was no way to fix the problem. I tried everything. Only after upgrading to iOS 13 did the problem go away and never came back. I thought that was the end of it. I guess there was a structural change made to the configuration table for app network access so the problem was gone.
Now I encounter the same problem with iOS 14! Nowhere to fix the problem, but can only wait for the next system update.