This question: Linear bending of a mesh, asks for a clarification on formulas from a linked paper which in turn is paywalled in the ACM digital library. I was able to find alternative links to the paper via Google Scholar, but thought it would be good to raise the issue formally rather than edit & forget.
How accessible should source material be? Arguably, the ACM link is less likely to rot than some duplicate copy on a faculty web page. Is stability more important than accessibility? Is it incumbent upon readers to find alternative copies if needed?
Or maybe the problem is the question itself - i.e. it doesn't present enough information / context directly & depends too heavily on the paper in question. Link only answers are a problem, maybe it's too much of a link only question.