Custom Visual: PBI Desktop throws "An error occurred while rendering the report" error and freezes

OK, I think I have narrowed down the problem a little. For my dataViewMappings I am using the table mapping. I've discovered that I only get this error when I add a hierarchical into the Grouping value. I'll attempt to explain this with the following information.

These are my dataRoles, dataViewMappings & drilldown:

{
  "dataRoles": [
    {
      "displayName": "X Axis (Date)",
      "name": "xAxisDate",
      "kind": "Grouping"
    },
    {
      "displayName": "Y Axis (Value)",
      "name": "yAxisValue",
      "kind": "Measure",
      "requiredTypes": [
        {
          "numeric": true
        },
        {
          "integer": true
        }
      ]
    }
  ],
  "dataViewMappings": [
    {
      "table": {
        "rows": {
          "select": [
            {
              "for": {
                "in": "xAxisDate"
              }
            },
            {
              "for": {
                "in": "yAxisValue"
              }
            }
          ],
          "dataReductionAlgorithm": {
            "top": {
              "count": 1000
            }
          }
        }
      }
    }
  ],
  "drilldown": {
    "roles": [
      "xAxisDate"
    ]
  }
}

The pbiviz packages fine, however when I drag a date hierarchy onto the X Axis Grouping like so:

Then I get this error in PBI Desktop:

This is what my date hierarchy values look like:

Any ideas what the problem may be? My version of Power BI Desktop is Version: 2.87.1061.0 64-bit (November 2020)