I’m going to jump out on a limb here and make the assumption that you’re probably a Chrome user and before you went away you updated Chrome.
If so, you're probably the victim of a Chrome updater bug and your issues are not related to your Apple hardware nor a bug with macOS.
NOTE: If you're running Mac OS X El Capitan or later and have not disabled SIP, ...
Reset NVRAM or PRAM on your Mac
Settings that can be stored in NVRAM include sound volume, display resolution, startup disk selection, time zone, and recent kernel panic information. The settings stored in NVRAM depend on your Mac and the devices that you're using with your Mac.
Shut down your Mac, then turn it on and immediately press and hold these four ...
Regarding the first attempt to simply use unlockVolume, please consider trying this variation instead:
diskutil apfs unlockVolume /dev/disk3s1 -user disk
Your attempt to unlock using the UUID failed, because you failed to enter the complete UUID. I don't know if you typed it in manually or used cut-n-paste, but you've missed the last letter "C" in the UUID ...
Well I’m not expecting it as an answer but it’s a wild thing to try.
I encountered something similar when I forced shutdown my Mac when OS was probably doing something “important”. My guess is that the system recovery unmounted the volume to repair disk permissions and got interrupted.
My idea is to use some powerful disk partition utility (gpart) in ...
MacOS protects system level files as well as kext files. Maybe the following will help you. Please backup everything up and research it a little further before attempting making any of these changes.
To disable System Integrity Protection:
Boot into recovery mode and enter the following terminal command
Changing Kext Files
To allow ...
You have pretty much answered your own question.
Tried SSD on another system and it works, CHECK
Old drive works fine, so it's not the Mac, CHECK
This points directly to the only other piece of hardware you haven't tested elsewhere, the adapter. So, unless you can test that adapter and drive in another similar Mac I would say you should replace the adapter....
To attempt to back it up you could try starting in Target Disk mode & connect it to another Mac.
It is potentially safe - as you've checked the disk already with no errors - to simply overlay a new OS on top of the existing one without disturbing any other data. Run 'Install macOS' from the Recovery partition.