A couple of weeks ago, this site was subject to a sustained period of DDoS-resembling traffic appearing to originate from the Far East, which was causing the auto-scaling setup on the site's infrastructure to go wild, costing a lot of money, but also making the servers really unreliable to the extent that they would go down on a near-hourly basis.
Steps were taken to mitigate this traffic, but it looks as though those steps have had an unintended consequence of removing the ability to post images and embed third-party media and other content.
This is being worked on, and hopefully I'll have a resolution at some point this evening (Friday).