Harvard received the first plagiarism complaint in October. The investigation of the claims in that complaint came to its conclusion on December 9. Harvard said they supported her as recently as December 12.

Harvard University announced Tuesday that under-fire President Claudine Gay will keep her job — even after reportedly losing more than $1 billion in donations since her disastrous congressional testimony about antisemitism.

The Harvard Corporation — the university’s highest governing body — made its announcement Tuesday following night-long talks between Gay and university leaders, a source familiar with the decision told the student newspaper, the Harvard Crimson.

"As members of the Harvard Corporation, we today reaffirm our support for President Gay’s continued leadership of Harvard University. Our extensive deliberations affirm our confidence that President Gay is the right leader to help our community heal and to address the very serious societal issues we are facing,” the group said in a statement.

https://nypost.com/2023/12/12/news/harvard-expected-to-announce-claudine-gay-will-keep-job/

The Harvard Corporation expressed concerns about allegations of plagiarism in University President Claudine Gay’s academic work Tuesday morning, even as the board declared its unanimous support for Harvard’s embattled president, providing Gay with a path forward to remain in office.

“As members of the Harvard Corporation, we today reaffirm our support for President Gay’s continued leadership of Harvard University,” the board wrote in a University-wide statement on Tuesday. “In this tumultuous and difficult time, we unanimously stand in support of President Gay.” ... While the Corporation said it did not believe that the allegations amount to misconduct, it announced that Gay agreed to amend two publications.

“On December 9, the Fellows reviewed the results, which revealed a few instances of inadequate citation,” the Fellows wrote. “While the analysis found no violation of Harvard’s standards for research misconduct, President Gay is proactively requesting four corrections in two articles to insert citations and quotation marks that were omitted from the original publications.”

https://www.thecrimson.com/article/2023/12/12/corporation-raises-plagiarism-concerns/

That said, two additional complaints were submitted in December. One complaint was submitted on December 18 and the other was on December 29. I think the last one just happened to be the straw that broke the camel's back.

https://freebeacon.com/campus/fresh-allegations-of-plagiarism-unearthed-in-official-academic-complaint-against-claudine-gay/

https://www.nytimes.com/2024/01/02/us/harvard-claudine-gay-plagiarism.html