SSD failure or something else? Startup disk not working
I have a mid-2014 13" rMBP that's having some issues. It (was) running on High Sierra. I swapped out the SSD about two years ago with Samsung 970 eVO and it's been running fine. I'm pretty sure I used a Sintech adapter, which is the recommended one.
I noticed starting about a month ago that if I taxed the computer too much (i.e. too many tabs/applications) then the screen would go black and I'd get thrown an error message that required me to restart the computer. Now, the screen goes black and I get the error pretty much as soon as I try to do anything on the computer, and the black screen now defaults to a file folder with a question mark. I could boot into macOS, I just couldn't seem to use it for very long.
I read that it was probably SSD related, so I went into recovery mode and tried to repair disks/containers and got no error messages during First Aid - they were visible and I could click on them, so I can't imagine that it is actual failure of the SSD? I still had the issues, so I went ahead with trying to reinstall macOS via normal Recovery mode, which would have bumped my computer back up to Mojave. Upon the first try, I got to the Mojave installer and it got about halfway done downloading before going back to the flashing folder.
Upon the second try, I can't even get past the language selection screen in normal Recovery mode - it just goes straight to the flashing folder. Internet Recovery mode now shows me nothing when I click Startup Disk, but I think it's because it got messed up when the glitch occurred during the first attempt at reinstalling Mojave.
My question is, with these steps I've taken and observations made, is this an SSD/adapter issue, or is there something wrong with the other hardware inside of my computer? Would it be worth the time to make a bootable USB to try and resolve this -- especially if I can't even seem to get into Recovery mode?
MacBook Pro 13″, macOS 10.14