This in-depth qualitative inquiry about an individual teacher’s reflection on the practice of emergent remote teaching (ERT) in a multicultural EAP classroom in South Korea aims to explore the sources of and teacher’s response to communication disruption between the teacher and students under the COVID-19 ERT practice in Spring 2020. A total of 222 e-mails exchanged between the teacher-researcher and the students were analyzed to identify the cases of communication disruption. Adopting the notion of reflection-on-action, the teacher’s reflective commentaries were elicited to examine the sources of and teacher responses to the communication disruption over the semester. Thematic analysis of the two data sets to find the target themes identified two major sources of the disruption: technical limitations of digital tools used for ERT, and the lack of pro-activeness in institutional decisions. Pedagogical implications from the findings include implementing ERT at least over an entire semester period to ensure the minimum pro-activeness in the institutional decisions, and establishing an online teacher network within the institution so that more immediate hands-on collective knowledge about ERT can be built and shared with teachers in need.