I have a LAMP website which allows users to share a graph on Facebook. It was woking fine until May 1st but now whenever I try to share, I just get a grey box.
My site was using sharer.php to do the sharing and giving as the url a document which would generate a single graph, and in it's og:image and og:image:url tags I put a url which points to some code which generates an 800 x 400 png of the same graph. If I copy either url into a browser, they render exactly what I would expect, but if I post the same url to the Sharing Debugger tool, it gives me a blank image.
I have noticed that although clicking the Scrape Again button usually calls the url which renders the image as a png, every now and then it does not, but there is no indication as to why and the Scraped URL page shows exactly the page I would expect with the correct og:image tags.
I have tried changing from using sharer.php to the FB.ui 'share' method, but this has not fixed the issue.
I have also tried asking in the Facebook Developer Community but have had no response. I even tried to raise a bug with Facebook, but it won't let me.
This is driving me nuts. I just don't understand why it has suddenly stopped working. Have I missed something or has Facebook changed anything in the Sharer functionality? Is there any other way to debug this ?
Update: After a lot of tinkering I have found out that this only affects my account, and it affects anything I share on Facebook, not just things from my own site. Furthermore, it's only the preview of the shared page which is not working. What actually gets posted to Facebook is the correct image. I have tried multiple PC's and multiple browsers and it always fails even if I switch off all anti-virus/anti-malware/firewalls etc. Bizarrely, if I share from my phone, it works!