Please have a close look at this article. There are several papers on this matter of challenges of PBL. However, I think PBL is better for my students ti achieve deep understanding, beyond shallow transmission of knowledge.
"Learning in PBL environment increases motivation and the probability of learning by deep understanding in contrast to passive knowledge transfer. Yet, the use of Problem-Based Learning also inherits certain challenges that can harm the positive impact of this alternative learning approach. The aim of this paper is to shed light on those aspects that are crucial to make PBL work. In the literature, the importance of the role of tutors and well-suited assignments are emphasised. This paper reflects on those aspects by drawing on the experience from the Bachelor European Studies at Maastricht University, but also discusses additional challenges like group dynamics and communicative skills."