Customer Error while Accessing PDF on UACP

One of our customers has raised an incident quoting issues with accessing a security guide on the help portal. Whether they use the relevant link via a pdf or enter it directly into the browser, they get the error "We're sorry, but this content is not accessible."

My understanding is that this is a user issue because we have tried the link and are able to access the document without issues. However, I would like to confirm this before responding to the customer. Are there any other possible reasons why this error could be coming up when accessing a pdf on the help portal?

Thanks.