Comment 1 for bug 1901077

I am testing this in a VM, and the functionality appears to work for the most part: all my cookies were indeed deleted, except for one (www.nytimes.com), so there's something fishy indeed.

Do you have the "Preload pages for faster browsing and searching" option enabled (it is on by default)? This feature advertises that preloaded information can include cookies.

Also, is your previous browsing session being restored when you launch chromium? That would load all previously loaded pages, and thus most likely write cookies to disk.