It seems not possible to upload a picture anymore across several StackExchange website.
It fails with "Failed to upload image; couldn't reach imgur" although the host i.stack.imgur.com is responding properly.
Other users confirmed the issue.
One of our ISP links to the NY data center was flapping which meant any traffic in or out of the data center to certain parts of the world was not being routed correctly. That affected our connectivity to Imgur who hosts our images. For now we've disabled that link and all traffic is being routed over our other ISPs