Since Complex Problem Solving (CPS) skills represent a key competence for educational success, they are of great relevance for learning analytics. More specifically, CPS serves as a pertinent showcase for addressing a crucial existing gap contemporary education is facing, the gap between students' ability to acquire and subsequently apply knowledge in uncertain situations, which are increasingly important in the 21st century. While the CPS process incorporates both the acquisition and application of knowledge, many earlier studies have focused on identifying the factors relevant for success in knowledge acquisition. Given the dearth of existing research on factors influencing a successful transition between both CPS phases, we investigated the rates of successful and unsuccessful knowledge transition over the course of nine CPS items in a sample of N = 1151 students in 9th grade. Results showed that many participants were unable to transition their knowledge from the acquisition to the application phase, which was presumably due to an inefficient mental model transfer. Furthermore, the likelihood of students being ‘lost in transition’ was higher in more complex items. Implications are discussed in light of learning analytics, and particularly with regard to the factors to be taken into account by future CPS training programs