Office.js Excel Online > chart.getImage() errors

Summary: Some charts (when not the first chart), cause errors in Excel Online with chart.getImage().

Usage scenario: I use chart.getImage() to get the base64 encoded image so charts can be programmatically inserted into Word/PowerPoint documents. It is used in the Excel-to-Word Document Automation Add-In.

There is never an issue with Excel for Windows or Mac. Issue only occurs with Excel Online.
Error only occurs with some chart types, such as Pareto, Funnel, and common charts with some customization
Error is not consistent: cannot always predict it, same chart, same code sometimes works fine.
Position of chart seems to matter. First chart added never seems to produce errors.
Type of error is not consistent. Is either: UnsupportedOperation, GeneralException, or ValueNotLoaded.
Method details are here: https://dev.office.com/reference/add-ins/excel/chart

Is this a bug that can be fixed? Is there a known workaround?

Simplified Code that can reproduce error (in Script Lab):

function run() {
  Excel.run(function(ctx) {
    var chart = ctx.workbook.worksheets
      .getItem("Sheet1")
      .charts.getItem("Chart3");
    var image = chart.getImage();
    return ctx.sync().then(function() {
      var data = image.value;
      console.log("Success: " + data.substr(0, 100));
    });
  }).catch(function(error) {
    console.log("Error: " + error);
    if (error instanceof OfficeExtension.Error) {
      console.log("Debug info: " + JSON.stringify(error.debugInfo));
    }
  });
}

Sample Error Returns (I've encountered 3 types from this getImage() issue):

{
  "code": "UnsupportedOperation",
  "message": "This operation is not implemented.",
  "errorLocation": "Chart.getImage",
  "statement": "item.getImage(undefined, undefined, undefined);",
  "surroundingStatements": [
    "var workbook=context.workbook;",
    "var worksheets=workbook.worksheets;",
    "var worksheet=worksheets.getItem(\"Sheet1\");",
    "var charts=worksheet.charts;",
    "var item=charts.getItem(\"rpt_Chart3\");",
    "// >>>>>",
    "item.getImage(undefined, undefined, undefined);",
    "// <<<<<"
  ]
}

{
  "name": "OfficeExtension.Error",
  "code": "GeneralException",
  "message": "An internal error has occurred.",
  "traceMessages": [],
  "innerError": null,
  "debugInfo": {
    "code": "GeneralException",
    "message": "An internal error has occurred."
  }
}

{
  "name": "OfficeExtension.Error",
  "code": "ValueNotLoaded",
  "message":
    "The value of the result object has not been loaded yet. Before reading the value property, call \"context.sync()\" on the associated request context.",
  "traceMessages": [],
  "innerError": null,
  "debugInfo": {
    "code": "ValueNotLoaded",
    "message":
      "The value of the result object has not been loaded yet. Before reading the value property, call \"context.sync()\" on the associated request context.",
    "errorLocation": "clientResult.value"
  }
}

this is potentially a bug and the team is working on fixing it. Will update this answer as the fix becomes available. thanks! Juan.