Open Source Software (OSS) supports modern digital infrastructure and industry, making the ability to contribute and collaborate in OSS communities an increasingly important professional skill. Participating in OSS gives students valuable real-world software engineering experience, but also introduces distinctive challenges. In this work, we investigate the barriers university students encounter when contributing to OSS projects. We qualitatively analyze experiences from an advanced master-level software engineering course at a European university and systematically map those experiences to existing barrier frameworks. Notably, we identify two barriers not described in prior work: Conflicting Mentor Guidance'' andCommunication Channel Ambiguity''. By combining project characteristics with student reports, we also find that commit frequency is a more reliable indicator of contribution success than project size or age. Our findings show how barriers interconnect and compound for time-constrained student contributors, with interpersonal barriers often triggering or exacerbating technical and process barriers. Students who selected projects based on personal interest achieved higher success rates, underscoring the role of intrinsic motivation. We conclude with implications for practice: students should choose projects aligned with their interests and with active maintainer engagement; educators should use vitality metrics and prepare students for common barriers; and maintainers should prioritize timely communication and mentorship.