On June 4, the Lancet, the British medical journal that is one of the most prestigious scientific publications in the world, withdrew a paper that had been one of the most consequential in the novel field of coronavirus studies.
The peer-reviewed paper, which the Lancet had published on May 22, said that treating COVID-19 with the antimalarial drugs chloroquine or hydroxychloroquine raised the heart-related death risk for COVID-19 patients in the hospital without showing any benefit. The second paper was retracted from New England Journal of Med (NEJM) a pre print has also been off loaded. Plase peruse the link below for a more detailed version answering your remaining Qs. https://www.sciencemag.org/news/2020/06/whos-blame-these-three-scientists-are-heart-surgisphere-covid-19-scandal
Retraction Watch have a dedicated list for retractions pertaining to COVID-19. The reasoning given by the journals is usually available in a short article for each paper they have in the database.
Overall, the number of journals that report retractions has grown. Since the paper in question will be retracted from print and online versions of a journal, and any associated databases, it would be logical to assume that the journal’s editor or editorial board would make the decision to retract, but that is not always the case. Tracking the reason for a paper retraction can lead to different members involved in academic publishing, it could be the authors or co-authors retracing the study, journal editors issuing a retraction after complaints from readers, editors-in-chief issuing retractions because of extensive issues reported in the studies, or journal boards issuing retractions. In the case of COVID-19, clinical and treatment cases are more recurrent cases of retraction in my perception.