The paper is a contribution to the study of miscommunication in native–non-native speaker (NS–NNS) conversations. It analyses pronunciation-induced communication breakdowns (CBs) found in video-recorded face-to-face tandem conversations held in English by 21 pairs of students, each consisting of a native speaker of English and a native speaker of French (SITAF tandem corpus; Horgues & Scheuer, 2015). These NS–NNS interactions are shaped by specific linguistic, discursive, intercultural, and psycho-affective characteristics of the Tandem learning framework. We draw on our previous research which showed that pronunciation was the single most important linguistic factor behind CBs arising from the speech of the NNS in a debating task. We now aim to look for possible task effects on the frequency and nature of the CBs by comparing two collaborative speaking tasks in English. Our results confirm that the amount and types of CBs are indeed shaped by the tandem learning setting and tasks, and that pronunciation is the main impediment to the intelligibility of NNS English speech in the corpus. We hope our study contributes to a better understanding of the communicative impact of L2 pronunciation in authentic NS–NNS exchanges.