From the description at the beginning of thisLittle Office of the Sacred Heart of Jesus ... assembled by Fr. Croiset ... it seems that the author might possibly be one of Fr. Eudes, Fr. Gallifet, and Fr. Croiset. It isn't clear from this source.
It's clear that Fr. Croiest wrote the book for Devotion to the Sacred Heart from which I gather the Little Office of the Sacred Heart of Jesus was developed.
I also saw the link you posted while doing my research. Most of the sources I found today don't really indicate the author either. This source did have a very interesting history written about the involvement of Fr. Croiest and St. Mary Margaret Alacoque. Devotion to the Sacred Heart
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