Are you sure the Sumatra preview handler (NOT the standalone Sumatra application) supports CBZ files?
As far as I can tell, it doesn't. It only registers itself for the .PDF extension, and if I force it to handle .CBZ I just get a grey background in both the preview pane and the standalone viewer.
When you say it's working in the Opus viewer, are you certain it's the Opus viewer and not the Sumatra application? Because I get the same results in both the viewer and the preview pane. It only works in the Sumatra app itself:
Beyond that, it's probably something you need to ask the Sumatra developers about. We can ask their viewer to try to display any file within one of our windows, but what it ultimately does is up to it.
If I edit the registry to make File Explorer try Sumatra for .CBZ files, the same grey window is the result:
So I think you're talking to the wrong people about this problem. You need to talk to the Sumatra developers.