From a Google search the source of that message seems to be ApplicationInsights which is in-line with your statement about the application continuing to work as if this theory is correct that component is just for collecting information and simply chooses to truncate the URL.
If the application is using the implicit grant then authentication responses (which would include tokens) are delivered by default in the fragment component of the URL so that would be one possible explanation. The resolution would be to consider using a different response mode that does not include the tokens (which would likely be the culprit) in the URL.