I contacted with some Samsung support centers and they said that factory reset after OTA update will fix the issue. I've also tried everything, flashed official rom, performed factory reset, removed sd card etc. etc. like most of you. None of them helped but this factory reset after OTA method REALLY works.
Steps I did are:
- Downloading OTA update and applying it,
- Performing factory reset and formatting sd card in options menu,
- Restarting in Recovery mode and performing wipe data and cache.
I did it a couple weeks ago and waited a while to share in here. During this time, I restarted the device several times, plugged/unplugged sd, install/remove apps etc. And now it's still in "Normal" and never changed to "Modified" even 1 time (thank god, finally). Btw I'm also using 64gb sd and there are several musics, videos and images in it.
The strange thing is, they said: "We recommend all our customers to perform factory reset after each OTA update". Yeah, it sounds really stupid. We hope they find a permanent solution asap because its nonsense to loose datas that cannot be saved without root access after every update.