That's strange. Does the problem go away when you reload the document and re-open the add-on?
The message is a very severe message and it will definitely cause problems. It has nothing to do with your internet connection. It means the add-on can't access the document through Google's servers and pretty much nothing will work. Muting is not an option.
The add-on internally tries several times to connect to Google's servers becfore it gives up and shows the message.
If this was not just a temporary issue, we need to debug that in more detail.