See attached screenshots. Epiphany's "Clear Personal Data" UI, which uses WebKitWebsiteDataManager, says I have no cookies, localstorage, or indeed any website data at all for gitlab.gnome.org. However, I see it in the web inspector. Looks like WebKitWebsiteDataManager is lying. Similarly, I see no cookies or website data for gnome.element.io. In the web inspector, I see that one has stored cookies, localstorage, and IndexedDB. My first thought was "maybe it is using the top privately-controlled domain" (base domain) which would be gnome.org. But it shouldn't be, and it is not. I see cookies stored for gitlab.freedesktop.org, for example.
Created attachment 432473 [details] Something's missing here!
Created attachment 432474 [details] Web inspector