We have a customer reporting that sometimes when a users Web Client session times out and then they try to navigate, rather than getting redirected to the Login page, they get the below error.

If they click the "Click here to go back..." they get taken to the Login page and are able to proceed normally, but it is just confusing and irritating that the user gets shown the error and must manually click the go back to re log in and continue.  They are reporting that this is happening more and more.

Since it does not happen every time a timeout occurs, are there any ideas on how to track down what is causing this error to be presented and how to prevent it?