This situation can occur if:
The administrator has created a message in which he says that a new document is available (from the knowledge base, for example) and attaches a link to it.
Further, the administrator gave users access to this message, but did not grant access to the new document.
In such a scenario, users will read the message and follow the link, but since they do not have access, there will be a blank screen and a 404 error.
How to avoid ?
Always, when providing links to materials, open access for these links as well.