I was having this same “No Channel available” message with no chat after updating to the latest version of this plugin and found the following error in my error logs:
WordPress database error Unknown column 'chat_recipient_id' in 'where clause' for query SELECT * FROM wp_wise_chat_messages WHERE channel = 'global' AND (chat_recipient_id IS NULL OR chat_recipient_id = '') ORDER BY id DESC LIMIT 100
Sure enough, there was no ‘chat_recipient_id’ column in the ‘wp_wise_chat_messages’ table! I deactivated and reactivated the Wise Chat plugin and the issue was fixed! The ‘chat_recipient_id’ column had been created and the chat loaded fine after that.