I had "Warning Camera Failed" problem on my SM-G900SW (S5 in Canada), along with some other weird problems.
After reading an announcement from Samsung that the problem is ROM related download the stack image for my device/provider from Samfirmware and re-flashed the phone.
The problem went away, and so did some other issues.
This is definitely a software issue IMO.
To add to this, after I flashed the stock firmware everything was fine for a few days until suddenly I was unable to turn on Bluetooth. So the camera still worked, but bluetooth stopped working.
I took the phone back to the store, showed them the problem and exchanged. In the process of exchanging it I did a factory reset to remove personal data. When the reset was done, I turned it on to make sure my accounts were gone, and lo and behold the camera and bluetooth worked again.
I still went through with the exchange since this does seem like a problem related to the storage memory becoming corrupted after a bit of use.
I've had the new one for 3 days, and so far no problems.
---------- Post added at 11:34 AM ---------- Previous post was at 11:33 AM ----------
I've read that it only happens to US version of the phone when the user installs another camera app.
Seeing as I'm Canadian, nope.