If you delete a teacher's account in Sdui, all the groups in which this person was the only group administrator are automatically set to one way. The remaining group members are no longer able to use this chat.

This is a safety measurement, meaning that students in a class or group are not able to write to each other and use the chat unsupervised.

Existing private chats with the person will continue to exist, to ensure that no information is lost. Since the profile no longer exists, the chat is renamed to "Unknown conversation".