VK - how to find out what happens during an Open Graph data request?

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In general, we blocked VK at work (yes, I know we are just animals), now it has been unblocked (that is, you can enter the site without problems), but when publishing blog entries (WordPress), the Open Graph markup is not pulled up. Has anyone encountered this kind of troubles? Maybe we haven't unblocked some port that can be used by VK for GET meta markup? Honestly, we just can’t understand anything anymore, metadata is being pulled into all social networks with a bang, but from VK it’s a problem.
Thanks to all.