“Mastery Learning: A Psychological Trap?”, William F. Cox Jr, Thomas G. Dunn1979 (; similar)⁠:

In spite of all its announced advantages, the implementation of mastery learning instruction often falls short of theoretical expectations.

As discussed under the four major characteristics of mastery learning [systematic design of instruction/instructional correctives/ample time to learn/clear criterion of mastery], these implementation weaknesses pose serious problems for unsuspecting students, teachers, and instructional designers alike.