Is my SSD fried?

2011 MacBook Pro 8,2 >Replaced HDD with SSD in Feb 2018. About 2 weeks ago I was unable to login to computer user account after low battery shutdown and was unable to login via known password from either user. I noticed a new user account had been setup with name formatted like recovery key. I tried to reset password via Terminal and it wouldn’t accept password from either user and got message that iCloud had not been setup (although it definitely had). I ran Apple Hardware Test and found no errors. So I decided to just erase SSD and reinstall macOS using Command-R.

Erased SSD volume via Disk Utility and then completed successful OS Reinstall of High Sierra. Setup new user account and opted to use FileVault with iCloud recovery but not iCloud backup. Selected option to restart and install updates via App Store when prompted. Installed updates and restarted a time or two.

Logged in under new username and got stuck at gray prohibitory screen. Restarted laptop again and went into Command-R recovery mode using Internet Recovery. Used Disk Utility and verified SSD volume was ok. Repaired via Disk Utility for good measure. Restarted again in normal mode and got stuck at gray blank screen, before user login screen appeared. Restarted again in Command-R recovery mode using Internet Recovery. Again verified and repaired SSD in Disk Utility. Noticed no boot drive listed under Show All Devices.

Attempted to erase SSD in Disk Utility to install again without FileVault encryption and got a disk object invalid or unable to serialize error. Attempted to repair, but option was grayed out. Selected Show All Devices option and SSD disappeared from view. Opened Terminal and ran diskutil list and was unable to find SSD (disk0 was not listed). Back to Disk Utility and still nothing available, so restarted again under Command-R recovery mode. Different MacOS Utilities window opened, with same options except older (Reinstall option was for Lion, not High Sierra). SSD still not showing up under Disk Utility or Terminal list command. Restarted again to same MacOS Utilities window and Disk Utility showed SSD. No option to verify or repair volume. Terminal list showed SSD (as /dev/disk0). Attempted to use Terminal to verify disk0s2 (s1 was EFI), but got error starting file system verification for disk0 unrecognized file system (-69846). Tried to use Terminal to unmount and re-mount the disk before attempting another verification and repair with diskutil eject /dev/disk0 and got an error that the command timed out. Tried again and got an error that it was unable to find disk. Terminal diskutil list then also failed to show disk0.

Bought a USB to SATA adapter and tried to boot via USB to see if problem is a bad SATA cable. Got nothing but a solid gray screen for several minutes, with no ability to choose boot drive, but suddenly the user login screen appeared. I tried to login to my profile, and after it appeared that the password was accepted, it went to the gray screen with a prohibitory symbol.

I then realized that I still have my old HDD that I replaced with the SSD, so I tried booting from the HDD via USB, and it worked. I was able to successfully login and see everything that was there when I migrated from the HDD to the SSD a few years ago. Does this confirm the SSD is fried or is there something else that could be causing the problem? My SDD is still under warranty, and I'm trying to avoid the $ for a diagnostic appointment if possible.