Since April 11th 2016, facebook cannot get og:image metatag of our articles.
This is workaround to get facebook scraped og:image metatag.
Go to: https://developers.facebook.com/tools/debug/sharing/
Paste URL to debug, then click Debug button
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| Facebook: Sharing Debugger |
Scroll to end of page, click Scrape via API
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| Sharing Debugger - Scrape via API |
In Graph API Explorer screen, click Submit button
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| Facebook Graph API Explorer |