Popup Error message while using Message feature

While using the Message feature, at various times users will receive a popup error message box with the following:

• Error | Syntax error, unrecognized expression.
• TypeError | undefined is not an object (evaluating 'a.lastmessagedate)
• TypeError | Cannot read property 'lastmessagedate' of undefined

The feature continues to work after closing the error message popup.

Site is currently 3.8.3+