@mymothersdaughter: If you look at your list of installed plugins, do you see any plugins that are version “1.3.3” below the description? The problem might be that another plugin set a version number in your database, without specifying what it is for. I do see at least one non-free plugin that is currently version 1.3.3, called “Responsive Flip Book WordPress Plugin”, but I haven’t used it myself, so I can’t see if this is the problem. Unfortunately, turning a plugin off might not remove that record — but finding the version number would confirm that another plugin might have been the cause.
(I’m not affiliated with Sucuri, but I found this problem interesting.)
@yorman: In sucuri.php, in the function site_version(), it checks get_option(‘version’) first, then checks for wp-includes/version.php — my recent WP installs don’t have a ‘version’ record in the wp_options table, so maybe that was an older standard? (Unless it’s used in multisite, which I do not use.) If it checked version.php first, or if it used get_bloginfo(‘version’), that might solve the problem if this is caused by another plugin.
Edit: Sorry for interrupting — I didn’t see your newest post before I posted. But I hope this helps narrow down the issue!