SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2jm34q08d9t.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
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      "cw-f4afe214-3ebe-4b81-8fb2-7d3bc9e86e41"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-33fb0db1-3560-4589-82f7-04b18975f278",
    "manifestId": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2jm34q08d9t.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f4afe214-3ebe-4b81-8fb2-7d3bc9e86e41",
    "loadedManifest": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2jm34q08d9t.json",
    "canvasIndex": 2,
    "allowMaximize": false
  }
}