I spent my early phd years working on the missing baryons, and it's a really interest topic. Theoretically the problem is solved, and hopefully in the next few years newer X-ray telescopes and local FRB detections will confirm the these predictions which are - the baryon's aren't missing, they are just residing at temperatures and densities which are currently hard to detect. I think the research problem should probably be termed "the unobserved baryons", since nobody believes they are missing, but unfortunately academia loves sensationalism as it leads to funding and citations.