Using Facebook's Object Debugger, I've found that Ographr outputs
og:url as it is according to WP (without a trailing slash to prevent double-slash in permalinks). This causes a "Circular redirect path" and a discrepancy between
rel='canonical', at least if WP is in its own directory.
WP/Site Address is "http://www.example.com/wp" (in settings)
rel="canonical" is "http://www.example.com/wp/"
og:url is "http://www.example.com/wp"
The fix is to just append the trailing slash when outputting
is_front_page() || is_home() || is_404() and trailing slash isn't present.