I have a bit of an odd problem with something I wrote. The paper was once published, on an institutional website, but it's no longer there. It was written while I was in the Army, and published on the Training and Doctrine Command (TRADOC) website, back in 2014. A check of the URL (listed on my resume from when I was job hunting when I retired from the Army) now comes up with "File not Found." Goggle searches for the paper's title can't find the paper either.

So, what's the proper way to list something like that on a CV? Unpublished work? De-published work (because it was published, but then not)? OK, I'm being tongue in cheek there. Out of print?

I think it got 'disappeared' because the Army concept document (Army Operating Concept 2014) that it was intended to support is no longer current, having been revised/replaced by newer versions I think twice since then.

You might list it and say something like "Published on TRADOC website 2014. No longer available online."

You could list it on arXiv yourself, and reference it there.