Like single chats, group chats are end-to-end encrypted in Threema. For privacy reasons, groups are not managed on our servers but directly on users’ devices. Since there is no information concerning group compositions stored on the server, groups can become asynchronous, e.g., if a user restores a data backup or is absent for an extended period of time.
If a group is asynchronous, we recommend resynchronizing it first. Only the creator can initiate a synchronization (in the group’s detail view). Should the problem persist, please remove the group member due to which the
group became asynchronous (see above), and add them again.
You can access a group’s detail view by tapping on the title bar in the group chat.
If some members cannot see messages in a group chat, it is usually because they have activated the “Block Unknown” option. Disable the “Block Unknown” option in “Threema > Settings > Privacy” to receive all group-chat messages.
