Results not loading in Wiql Playground when selecting certain columns in query

Describe the bug
We are getting a "Loading Workitems..." message with no results returned when we attempt to execute a query where we select the following columns:

• System.Id
• Custom.TargetCompletionDatee

Environment:

• Browser = Chrome and Firefox
• hosted (Azure Devops)
• Installed version: 2.1.69 (Latest)

Screenshots

To Reproduce
Steps to reproduce the behavior:

1. Go to Wiql playground
2. Enter the following query:
3. SELECT
   [System.Id],
   [System.AssignedTo],
   [System.State],
   [System.Title],
   [System.Tags],
   [System.WorkItemType]

FROM workitems
WHERE
[System.TeamProject] = @project
AND [System.AreaPath] UNDER 'CSG-Wk-Mgmt\RMDM\Singleview'
AND [System.WorkItemType] = 'Bug'
AND [System.ChangedDate] > @today - 2
ORDER BY [System.ChangedDate] DESC
4. Click Run.
5. The "Loading workitems..." message appears and stays there. No results are returned.
6. Remove the [System.AssignedTo] line from the SELECT statement and click Run.
7. Results are now returned as expected

Expected behavior
Query should return results with any valid fields in the SELECT statement.

Additional context
Clicking on the "Open in queries" button to execute the query in ADO results in a successful query.

Start by reproducing the query in the Wiql Playground using the SELECT fields in the issue, then compare its behavior with the successful Azure DevOps query. Trace the query execution and result-loading entry point to identify why a valid field leaves the interface on "Loading workitems..."; done means results load for queries containing that field.