Update 01-09-23
Facebook have now fixed the issue so the share buttons are working normally again. 

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Facebook seem to be having an issue with their share button. When something has been shared once, the button fails to load again, so I assume it is connected to the Facebook share counter.

This is all handled by Facebook servers, so it's just a case of waiting until they get around to fixing it, hopefully no too long.

It doesn't affect the NFED in any other way & ads/events can still be shared from the NFED Facebook page or using other sharing methods.