Not being notified of incoming chat

We have had Zendesk Support and Zendesk Chat installed for years without problem.

Yesterday, we started getting notifications of incoming chats, but the customer was not receiving any of our chat responses. (We verfified this by initiating a chat as a customer.)

We turned off chat, presuming it was a system issue.

Today, we are no longer getting any notifications of any new chats. They are just queuing up without any notification to any of our agents.

Our agents have not changed any chat settings.

Is this a known issue currently or is there something we have to do? We have tried on multiple computers (Mac, PC) and multiple browsers.

Thanks!