SM-N910G Stock - Contently freezing, restarting to download mode and data lose

Hey all,
I found few similar threads, but none of the solutions worked for me. So here's my situation

Problem : N910G Singapore Starhub, used for more than 1 and half years without major issues. Suddenly started to randomly freeze and then restart.
Got worse very quickly. Started to get freezed at Samsung logo. Most of the time had to remove the battery to re-try booting.

What I've done so far:

1. Cache cleared -> Didn't work
2. Factory reset -> Was ok with less lag (Freezing) for sometime, then same again
3. Installed TWRP. Flashed PIT file. Following an XDA post, flashed Samsung stock Android 6 released to India -> Was ok for couple days, was better than 5.1 in terms of responsiveness and battery life. After few days, again freeze. restart
4. Flashed with stock 5.1 released for the correct region. -> freezing, restarts. Wifi passwords are not getting saved (Have to re-enter upon restart). Restarts end up in download mode. very rarely passes the Samsung logo
5. Rooted and tried to change build prop ro.securestorage.support (or something similar) and see whether passwords are getting saved -> Still passwords are not getting saved. /efs is accessible.

Now the device never boots properly. Some apps are missing after restarts. Always ends up in download mode. Recovery is working fine though.

You guys have any idea what else I should try before throwing this away?
Thanks in advance.

from xda-developers http://ift.tt/1NNhADG
via IFTTT