Link to the story:
https://phys.org/news/2023-10-group-stars-vanishedastronomers.html
From the article: A third idea is that they weren't objects at all. Palomar Observatory isn't too far from the New Mexico deserts where nuclear weapons testing occurred. Radioactive dust from the tests could have contaminated the photographic plates, creating bright spots on some images and not others. Given similar vanishings seen on other photographic plates of the 1950s, this seems quite possible.