Galaxy S5 G900V startup failure with inconsistent symptoms making troubleshooting difficult o/

My Samsung Galaxy S5 suddenly and quickly started deteriorating a few days ago. I did also install a software update from Verizon about a week ago, but what's odd is how the symptoms worsened gradually. (Why would software do that?)


It started with occasional, random power-offs. No worries, I just rebooted.
Later, some of those times I started seeing "SECURE FAIL: KERNEL" in red. 1 or 2 extra reboots, though, and I'd be good to go.
Yesterday, the phone shut off a few times, taking more reboots to get things going.
Now, sometimes the power button doesn't respond (not even the vibration). When it does, sometimes nothing shows up on the display. If a display shows, it might hang on the Samsung GALAXY S5 "Powered by Android" loading screen—but that's not as common.* More common is simply going to that "SECURE FAIL: KERNEL" screen. I've been rebooting for an hour now—probably 20+ times—with no success in getting a full boot.


* This screen actually says "Custom" as well, with an unlocked padlock icon. But I've never rooted a phone, nor done anything "custom." I read something about ART vs. Dalvik and that it's normal for this phone. Plus, that started showing up months ago, so I'm guessing it's unrelated.

Given the variety of symptoms—from the power button not responding to this "SECURE FAIL: KERNEL" message, and also the gradual degrading of successful reboot attempts, am I correct to conclude that this is more likely a hardware issue than software, e.g. the update to Lollipop, if that's what it was?

Some other notes that may contain clues for the more experienced:


I did manage to get into recovery mode once, and wiped the cache.
The other two attempts left me with a screen saying "SECURE FAIL: RECOVERY".
Sometimes the phone seems to start up by itself after 10+ minutes of not being touched, having a black display, and no indicator lights.
While plugged in and in the above state, I don't see the green battery charging animation. Maybe that means it's not really "off" but stuck in some software block or loop.
Once I did see the battery animation, and the battery was at 88%, so I think the battery's okay.
This is a S5 G900V that I purchased new from Verizon in October 2015.


Thanks in advance. I wish it would start up properly just once so I can get some data off the phone's memory.



An interesting development.

While typing this post, it got past "SECURE FAIL: KERNEL", but froze at the Samsung logo animation. Then, the display went black, while the blue indicator light stayed on. A few minutes later, the phone restarted itself, passed the Powered by Andoird screen as it usually does, and hit "SECURE FAIL: KERNEL." I rebooted again, and saw something I saw only once before, "SECURE FAIL: Modem."
I totally agree with all the symptoms you document. It reads like I would have wrote it. It seems many of us are suffering the same phone disease. Ultimately I ended up sending the phone to Samsung. They returned it unrepaired and stated the cost for repair  would be unjustifiable. Apparently, though, it can be repaired. I called Samsung, and, of course, talked to someone "who knows where". She did try and did say that an S7 root driver was installed into my S6. She said I could have done this while connected to my PC. Nope, the phone auto downloads updates. 
I don't understand why they cannot reflash the chip. I don't understand how I could be responsible for this and why I should have to purchase a new phone. 
Personally, I think Samsung sent the update without safeguarding that an older model would not auto download it. I think it's their fault and they are not taking responsibility. I didn't do this and now it's out of warranty, because of this unauthorised flash, irreparable due to cost. I'm screwed, we're screwed.

I'd like to see a class action law suit against Samsung and our providers. It smells of a conspiracy to make us upgrade $$$.

Gil