Plugin not getting the featured image

For some reason, the plugin recently stopped getting the featured image in certain kinds of posts (in this case, events created with the pluging All-in-One Event Calendar by Time.ly).
In some cases, it gets some random image it found on the page (gallery update, sidebar image, or whatever), and in those cases, I can just edit it and change for whatever image I want. But in others, Facebook won’t recognize any image, so I can’t even change that and the post has no thumbnail whatsoever.
I debugged it [https://developers.facebook.com/tools/debug/og/object?q=http%3A%2F%2Fstanakaticbrasil.com%2Fevent%2Fcastle-3-12-poof-youre-dead%2F] and it says:

Warnings That Should Be Fixed
Inferred Property – The ‘og:image’ property should be explicitly provided, even if a value can be inferred from other tags.

Parser Mismatched Metadata – The parser’s result for this metadata did not match the input metadata. Likely, this was caused by the data being ordered in an unexpected way, multiple values being given for a property only expecting a single value, or property values for a given property being mismatched. Here are the input properties that were not seen in the parsed result: ‘fb:admins, og:title, og:site_name, og:description, fb:app_id’

Shouldn’t the plugin create the og:image, specially since the post has a feature image (640px x 300px, btw)?
I tried adding the very same image to the body of the post as well. That did fix the thumbnail issue with Facebook (I just went back to the page and deleted the image right after FB recognized it as a thumbnail). But got these errors on the debug page:

Object at URL ‘http://stanakaticbrasil.com/event/castle-3-12-poof-youre-dead/’ of type ‘website’ is invalid because it specifies multiple ‘og:url’ values: http://stanakaticbrasil.com/event/castle-3-12-poof-youre-dead/, http://stanakaticbrasil.com/event/castle-3-12-poof-youre-dead/.

Warning: Errors That Must Be Fixed
More Than One OG URL Specified Object at URL ‘http://stanakaticbrasil.com/event/castle-3-12-poof-youre-dead/’ of type ‘website’ is invalid because it specifies multiple ‘og:url’ values: http://stanakaticbrasil.com/event/castle-3-12-poof-youre-dead/, http://stanakaticbrasil.com/event/castle-3-12-poof-youre-dead/.

It says nothing about the image tag, but for some reason, it’s reading the page url twice?
Any clue as to what might be the issue?

https://ww.wp.xz.cn/plugins/facebook-and-digg-thumbnail-generator/