Extended diagnostic error code 3

I just moved to a new SSD and when I tried to back up the old one using Acronis True Image, it found file system errors. chkdsk /r fixed some problems but that didn’t solve my initial issue, so I downloaded Sandisk SSD Dashboard and ran S.M.A.R.T. diagnostics. This is what it showed:
I know this SSD might be dead, since I bought it 2nd hand from an unknown source, it was cheap, and I used it for several years very extensively - but I would still like to know two things:

  1. what exactly does this error code mean, in more technical terms?
  2. is there a way to make a full image backup ignoring this error?

To clarify, I don’t have any problems accessing files on that drive, it seems to work fine as far as I can tell. The only problem I have is backup programs spitting out this mysterious file system error.