Using date field with Q&A

My dataset has a date field (date only, no time value in it) called "CallDate". I can see it in my Dataset, I can create a report using it like so: PowerBI Report Screenshot

On the Axis field, I set the CallDate to just "CallDate", because setting "Date Hierarchy" makes the user need to "drill down" and I don't want that, I want it to just be per-date as shown in that picture.

I can save that report fine, and I can even pin it to a dashboard.  But then Q&A doesn't work.  If you type a phrase like "average of AgentTime by CallDate", the "by CallDate" turns gray like it doesn't understand the request.

The CallDate is a date field in my data source, and I've tried shaping the query many different ways and even creating new date columns in PowerBI desktop, then publishing. But nothing I can do will make this report work correctly.

Example of the problem: PowerBI Dashboard Screenshot