Embed API console error: TypeError: e._previewPromiseResolve is not a function

Hello

We are using the embed API in our system. 

The console is complaining that this._previewPromiseResolve(); is not a function

This is the function its coming from:

_previewReady = () => { if (!this._previewPromiseDone) { this._previewPromiseDone = true; this._previewPromiseResolve(); } };

Any ideas to resolve this? Thanks