Brigham D. Madsen argues that B. H. Roberts lost his testimony.
Brigham D. Madsen, "B.H. Roberts’s Studies of the Book of Mormon," Dialogue: A Journal of Mormon Thought 26, no. 3 (1993): 83, 86
Is it possible then that Roberts could leave the impression in his public statements that he still retained his belief in the Book of Mormon while privately harboring the conviction that it was a product of Joseph Smith's very retentive memory and fertile imagination? Other people seem to be able to thus carry water on both shoulders. If belief in the authenticity of the Book of Mormon is the litmus test of orthodoxy, there may be a few and perhaps more than a few active but unorthodox Mormons who are followers of B. H. Roberts at heart.
. . .
In other words, and in the plain kind of language that Roberts liked to employ, there were no gold plates, there was only Joseph Smith drawing upon his creative imagination to formulate and write a work of fiction called the Book of Mormon. This preeminent Mormon intellectual and church authority was a conscientious scholar who was willing to follow wherever the evidence led him.