The filename with its path and the path in the browser (https://cloud.example.org/all_of_this?open=including_this) would be highly interesting here. If the actual data is too sensitive for you, could you look into creating a non-sensitive testcase that reproduces the issue for you?
If you want to dig a bit deeper, you could look into your browsers developer tools (Rightclick -> Inspect (element) -> Network) and look for the failed request and how it looks like.