This message is sent from ADS side. Here this is what I found from ADS Installation Guide:
As the installation manual mentions, A24 occurs in cases when blank image is enabled for non-interactive services, the ADS is moving the blank image to the server where the item was published, or in cases of cache duplication across multiple servers (normally seen for non-interactive services), where the ADS receives an image header for the item from a different (lower) server then the item is open on, the ADS will move (break stream and immediately failover) to the lower server.
When requesting a RIC, 'image' first delivers the full information of the issue to our application from our data source. That full information is "image". "Blank image" is a phenomenon that there is no information in "image".
In short, this message is generated from ADS' internal management situation.
Hope this helps.
The blank image mentioned by Nipat is generated by ADH to send blank image when there is no data in cache. If your service is interactive service, this is not the case but cache duplication.
Cache duplication can occur on a ADH load balanced configuration. The cache duplication is detected when multiple source distributes are sending updates on the same item. ADS would discard these multiple updates but if it does not, then it will attempt to redirect the request to the server with the lowest Server ID and send the A24 status.
If you need more details to understand which scenario occurred on this case, I suggest you contact TREP support team directly via Contact Us.