Pope Pius XII put Saint Frassati's canonization cause on hold in 1941. Why? What prompted the hold to be removed?

Pier Giorgio's cause for canonization began with great fervor but eventually did meet with opposition. The snag came in 1941 when anonymous allegations were submitted that questioned Pier Giorgio's reputation for moral integrity. Pope Pius XII acted on the side of caution and placed the beatification process on hold in 1942.

Many years later, Luciana Frassati (Pier Giorgio's sister) began discussions with Vatican officials in an attempt to clear the black mark from her brother's name. Her goal was not to have the beatification process reopened but, rather, to restore Pier Giorgio's good reputation which she felt had been unjustly tarnished by the anonymous allegations. However, as a result of her efforts, not only was Pier Giorgio's name restored, the cause was officially reopened by Pope Paul VI. It culminated with the beatification ceremony on May 20, 1990, when Pope John Paul II had the honor of declaring Pier Giorgio "Blessed." More details of the beatification process can be found in the book, "Blessed Pier Giorgio Frassati" by Maria Di Lorenzo.