Factory reset on a corrupted android OS?

[Android Central Question]

So about a few years ago, I tried to root my galaxy note 4 (sm-n910a, at&t version), but I guess it rejected the root because it instantly bricked my phone, to the point where I had to completely wipe it using android recovery. The only way to get my operating system back was to download it online and install it through my PC (I had to find the exact version for my phone as well, 5.1.1 at the time, because it rejected every single other version).

Everything seemed to be working fine, except that I couldn't install software updates on my phone anymore. It was permanently stuck on 5.1.1. It was a bit of an annoyance but I didn't think much of it at the time.

Fast forward to now, and I'm getting several signs that my OS may be corrupted. My phone is constantly freezing, crashing and restarting. Maneuvering through applications causes the phone to freeze for a few seconds before either restarting or crashing the app. I want to say it's definitely a software issue, but I did install a new battery recently and it was working fine for a few weeks, could that be the issue?

If not, I want to start over, but I'm not sure how, and I don't know if it's safe to do a factory reset on this OS. Is there anyway I can get a fresh stock version of an android OS that can also update?

Any help is appreciated, I'm pretty much desperate.

 

[Rukbat]

Restart to recovery (Home+Volume Up + Power). Wipe the System Cache, nothing else. See if that helps.

If not, https://forum.xda-developers.com/note-4-att/general/n910a-stock-odin-files-n910aucs2epk5-t3601576 has a link to EPK5. Whether that's the latest Note 4 ROM or not I don't know, but it's the only one I could find. (The A version of Notes is pretty well locked-down. So is the V version. And if Sammobile doesn't have the ROM [they don't for the A] you have to search.)

https://forum.xda-developers.com/no...hmellow-att-server-link-installation-t3407308 is a bunch of updates to get you up to Marshmallow (after a little more searching). I really doubt that you'll find anything later than 6.