Having the same issue with crashing, I did discover that it was one of my other plugins that was having issues with the newer versions of PHP (5.4 and newer) and crashing my site. Even after getting it working, there’s still other plugins that are causing smaller issues formatting and punctuation issues since they’re not compatable with PHP 5.4 and newer.
You might have better luck than i did, try disabling as many plugins as you can that will still allow your site to function, have your host update PHP and start re-adding the plugins one at a time until it crashes. Roll back PHP, turn off that plugin, and start turning other plugins on. . .wash rinse repeat.
But seriously facebook. . .huge pain in the butt for an official app. Why not adhere to the php standards virtually everyone is in wordpress is using? I’m having to either find another 3rd party app to work with Instant Articles or I get to rework literally thousands of articles to function and be formatted without certain plugins that I’ve been using since the inception of my site.