Browser console error on the Portal

[Mbellamy]

We are receiving a browser console error when opening a record producer in our portal.  The error reads "There is a JavaScript error in your browser console".  Upon reviewing the console there is a "Deprecated feature used" error which states" Unload event listeners are deprecated and will be removed."  

I am unable to identify where this error is originating from. Is there anywhere we can look to find the source of these errors?

Images attached.

[Brad Bowman]

Clear the Console log, then re-open the Record Producer to confirm that's the only / worst of the errors.  That one doesn't sound like it would cause problems - it's usually an onLoad Catalog Client Script calling a GlideAjax, or something that's different about that RP vs another that loads OK - a variable type that isn't supported in Portal, or some code in a Default Value.

[Mbellamy]

Thank you Brad.  I have deactivated all OnLoad Client Scripts and the errors continue to appear.  I have attached another error image from the browser console.   We are seeing an unhandled exception error in the console log.