My impression is that this happens when the loaded page is not “allowed” in the Extension Website Access section of the extension’s configuration.
Only the websites you choose have web content injected into them, and only those websites can be manipulated using the tab object’s properties, such as title and url.
Also, it seems that the Whitelist and Blacklist settings are applied “on top of” whatever is allowed by Extension Website Access.
First, access is limited by the Extension Website Access settings, then the whitelist and blacklist are applied.
My impression is that this happens when the loaded page is not “allowed” in the Extension Website Access section of the extension’s configuration.
Also, it seems that the Whitelist and Blacklist settings are applied “on top of” whatever is allowed by Extension Website Access.