A number of methods for large-scale agile development have recently been suggested. Much of the advice in agile methods focuses on teamwork. Prior research has established that teamwork quality influences project success both for traditional software development teams and agile teams. Further, prior studies have also suggested that teamwork quality may play out differently in large projects compared to small. We investigated the relationship between teamwork quality and project success with a survey of 196 project participants across 34 teams in four projects, replicating a previous study on single teams. The new data do not fit the previously established theoretical model, which raises several concerns. The observed effect of teamwork quality on project success operates differently across projects. We discuss possible reasons, which include disagreements on what characterises success in large-scale agile development, “concept drift” of teamwork quality factors, the possibility that interteam factors might have more influence on project success than intrateam factors, and finally, that our study design does not capture all relevant levels and functions. We conclude with a call for more studies on the quality and frequency of interaction between teams in addition to internal team factors to further advance theory and practice within large-scale agile software development.