Software architecture can be seen as a set of architectural design decisions (ADDs) that shape the resulting software solution. To make an ADD, stakeholders follow some organization- or team-specific group decisions making process. In this study, we aimed to advance the understanding of how ADDs are made by observing and learning how architects handle uncertainties in real-life settings. We employed a multiple-case studies research method. First, we examined the discussions in task management systems of three software engineering projects. Second, we conducted interviews with the projects’ software architects to investigate (a) uncertainties expressed in the observed discussions and (b) how those uncertainties are comprehended by their respective authors or readers. We systematically analyzed the interviews and derived different types of uncertainties as well as proposed a hypothesis that should be verified in the future work. Results of our qualitative study show how uncertainty is used and perceived by the software architects in the group decision-making process.