Disapearing report background when accessing online version

Hi all,

We have a report with a custom background.

The background can be seen on all networks except one particular organization's network.

Initially, the background is viewable inline with the report. After x amount of minutes, it stops being displayed until it is reuploaded. The background disappears after a short amount of time on all computers, browsers and servers Organisation wide.

Obviously, it's something being blocked on that network. But.. what exactly?