Regardless of what you believe, it is entirely possible for the data in your backup to be contributing or causing this problem. Just because it's 'always worked' doesn't mean that something hasn't changed regarding the data in your backup.
Let me explain it this way: The iOS version you are running (9.2.1) is currently running in millions of other devices. It is 100.00% identical to every other iOS 9.2.1 software running on all other iPhone 5S units. The only possible difference between them is a faulty installation of the software, which is fixed by reinstalling it.
The difference between the data in your backups from even a few days ago to now is far greater than any possible variance in the software between your device and any other 9.2.1 iPhone 5S. mathematically & technically speaking, it is far more likely that your data/backup is causing an issue than the iOS.
Stating that you see other people complaining about it isn't viable evidence or troubleshooting.
If I go to a hospital, I'm going to see a lot of sick people. It would be faulty logic to then deduce that there are also a lot of sick people out in the city.
If I go to a bar, I'm going to see a lot of people drinking. It would be faulty logic to then deduce that the same percentage of people out in the city are also drinking.
If I go to a prison, I'm going to see a lot of people behind bars. It would be faulty logic to then deduce that there are a lot of criminals out in the city.
If I got to an internet forum that specializes in helping people get technical assistance for their iPhones, I'm going to see a lot of people with problems with their devices. It would be faulty logic to then deduce that the same percentage of iPhone users in the world are having the same issues.
Once again: Make a backup of whatever you have on your device, then restore it as new via iTunes, then test the issue.
You came here for technical assistance, yes? Then, why are you unwilling to follow some simple recommendations?
Do you want to try to get your device to work properly, or do you simply want to complain and do nothing?