Onset of the Coronavirus Disease 2019 (COVID) pandemic has increased students' perceived burdens. The current study aimed to examine COVID-related changes and to identify potential factors that contribute to students' stress. Adopting a cross-sectional cohort-study design, we examined perceived stress and depressive and anxiety symptoms with a specific focus on the role of study-related variables such as perceived study-related demands, study-related resources, academic procrastination, and stress-enhancing beliefs. Two cohorts (Npre-COVID = 2,175; NCOVID = 959) were recruited at the same university and matched with regard to their propensity score (age, gender, semester). Compared with the pre-COVID cohort, university students in the COVID cohort reported more perceived stress, more depressive and anxiety symptoms, more academic procrastination due to fear of failure, more stress-enhancing beliefs, more distress due to the housing situation, and more perceived study-related challenges (Cohen's d = 0.15-0.45). A stepwise regression analysis identified depressive symptoms, procrastination due to fear of failure, general self-efficacy, increased study demands, perceived difficulties with self-organized learning, distress due to housing, and stress-enhancing beliefs as predictors of perceived stress in the COVID cohort. Findings suggest that the switch to online-only education increased the study-related burden for students, primarily due to exams being replaced by a greater amount of regular coursework and imposing demands on self-organized learning. Possibly, stress-enhancing beliefs and procrastination due to fear of failure might have been elevated due to less opportunity for social referencing and lack of felt social support by peer students. Experienced increased burden in students during the COVID pandemic was mostly accounted for by a lack of perceived individual resources rather than by an increase in objective study-related demands.