Whenever I'm editing a page's Composer attributes, they won't save or publish. No javascript errors come up in the console when I hit either of these buttons, but nothing happens (as if they lead nowhere).

The only thing that shows up in the console (not sure if it's related) is:
[Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, checkhttp://xhr.spec.whatwg.org/.

It was happening on a version of 5.7, upgrading to 8.2.1 didn't do the trick.