Nature: Millions of research papers at risk of disappearing from the Internet - An analysis of DOIs suggests that digital preservation is not keeping up with burgeoning scholarly knowledge.
(notable "he did not check whether items with a DOI were stored in institutional repositories, for example")
https://www.nature.com/articles/d41586-024-00616-5
(Study: "Digital Scholarly Journals Are Poorly Preserved: A Study of 7 Million Articles" https://doi.org/10.31274/jlsc.16288)