I'm having a similar problem.
I just got a Sprint Samsung S4. I rooted it to use Titanium Back Up for its multi profile features. Yesterday I received an OTA update. I installed it. Next thing I know wifi is completely gone. I kept getting a Knox notice. I tried to put an older pre-knox Android stock version via Odin. No go. So... i flashed a custom recovery (TWRP) to try and flash a stock android- again a no go (although my Knox counter now shows a lovely 0/1).
Just don't know what to do at this point. I've read through a ton of posts and tried several things, but nothing gets my wifi to start. Fortunately for me I have sprints unlimited data (as long as I'm on their network), but I like streaming via my wifi and want it back for when I go out of network.
Any help would be appreciated.