Background: Dealing with uncertainties is inherent in the engineering design process and often poses challenges for young learners. This necessitates providing learners with adequate support to navigate their uncertainties effectively. However, achieving this requires a deeper understanding of the factors influencing learners' uncertainty management processes. Method: In this paper, we analyze learners' framing of uncertain situations in collaborative engineering design tasks. Using the case study method, we explore two framing dimensions--epistemological and positional--to understand their impact on collaborative uncertainty management processes. Specifically, we examine how learners' framing dynamically shifts during uncertainty management activities by analyzing two contrasting cases from a sixth-grade classroom where groups tackled an engineering design problem, employing interaction analysis. Findings: Learners' epistemological and positional framings are intertwined, collectively influencing their own and their team members' uncertainty management actions. Additionally, contextual factors such as mentor intervention, early success, affect induced by prolonged failure, and time constraints can prompt shifts in learners' framing, both in productive and unproductive manners. Contribution: The paper provides nuanced insights into how learners' evolving epistemological orientations and positioning influence uncertainty management, offering practical insights into supporting learners' uncertainty management processes in problem-solving contexts such as engineering design.