Since the COVID-19 pandemic, there has been an increasing growing need for learning experience or instructional designers. As a result, online courses on user experience (UX) design for learning are in demand to prepare those much-needed professionals. This paper reports the first circle of educational design research (EDR) on such a completely online problem-based course using group contracts and peer-evaluations to promote collaborations. Multiple datasets were collected from a range of data sources from a graduate-level course and were analyzed by two researchers. The study yielded several meaningful results: (1) group contracts helped students work smoothly and keep goals focused on collaborative learning in PBL; (2) the instructor could facilitate the group formation process; (3) peer evaluations helped group collaboration and monitoring; and (4) collaborative technologies are critical for collaboration. The findings also revealed important design principles for collaborative learning in PBL that can be used in similar courses. In addition, this study provides a successful example of how to teach UX design in an online PBL environment, and sheds light on how to further improve similar practices while contributing to the limited body of research on UX design for learning.