If your chat bubble does not show as it normally did, this is more than likely due to your IT blocking the program we use. Below is a link directly to the product we use that you can provide to your IT dept. on what domains and IPs they need to allow so that you can use the chat bubble.
If the chat bubble is not showing for 1 user but is showing for others, the user might be on a different GPO than the other users. Your IT team could test by logging into their AD account on that user's computer and see if they have the chat bubble. Our system is not able to block the chat bubble for some users but not others.