Experiencing phantomjs errors - no version changes



We have an Ember app that we build regularly that will run a suite of tests via phantomjs.

We’ve been using v2.1.1 (the circleCI installed one) for a while now. We’ve had no changes in our app dependencies for over a week. Just yesterday our builds started timing out; after some investigation it was due to this error cropping up in our tests:

not ok 570 PhantomJS 2.1 - Global error: TypeError: undefined is not a function (evaluating 'obj.toString()') at http://localhost:7357/assets/frontend-vendor.js, line 16678

With no changes in phantomjs, nor node, nor any app dependencies, it’s not readily obvious what could be causing this. Has anyone seen this before or know any probable causes?