Started to see a message today "Due to an org policy change, you can enjoy a richer chat and calling experience. Continue your conversation here." We did not make a policy change.
Once I click "Continue", I am brought to the original chat with my external user. I am able to send messages to them but they are unable to send messages back. When they try to send messages back, they get an error of "The user is unavailable or offline. We've sent an email instead."
If the external user is in a group chat, they are able to receive and send messages.
