IE 11 error using Pnp.js for expand and

Question

I have run into a consistent error, that only appears to be appearing on IE, where pnp.js will not expand or select any fields upon a function call. This naturally causes issues

pnp.sp.web.lists.getByTitle(listName).items.select('Title,ID,IDCopy,Priority,Goal/ID,Goal/Title').expand('Goal/ID,Goal/Title').get().then(function(r)  { 
    console.log(r);
    // Other code here that does stuff.
});

on Chrome (and firefox and Edge) the result looks like the following:

Goal:
   ID: 
   Title: 
   odata.id: 
   odata.type: 
   __proto__: Object
[email protected]: 
ID: 
IDCopy:
Id: 
Priority: 
Title: 
odata.editLink: 
odata.etag: 
odata.id: 
odata.type:

In contrast: on IE, the result looks like this

   ArchiveG:
   Attachments: 
   AuthorId:
   ComplianceAssetId: 
   ContentTypeId: 
   Created: 
   EditorId: 
   FileSystemObjectType:
   GoalActi0: 
   GoalActi1:
   GoalId: 
   GUID: 
   ID: 
   Id: 
   IDCopy:
   LongTermBenefit_x002f_Quickwin: 
   Modified: 
   Notes: 
   odata.editLink: 
   odata.etag: 
   odata.id: 
   odata.type: 
   OData__UIVersionString: 
   Priority: 
   ServerRedirectedEmbedUri: 
   ServerRedirectedEmbedUrl: 
   Title: 
   ToDelete:

Needless to say, this breaks a bunch of later code, and as such must be fixed. Does anyone have any idea what I've done wrong?

Files used as polyfills:

 <script src="../polyfill.min.js" type="text/javascript"></script> 
<script src="../fetch.umd.js" type="text/javascript"></script> 
<script src="../pnpjs.es5.umd.bundle.min.js" type="text/javascript"></script>
 <script src="../jquery.sortable.js" type="text/javascript"></script>