URL query string parameter for filter results in error for embedded Power BI report in Salesforce

We embedded a Power BI report in Salesforce with Visualforce following Aaron Winters' instructions and syntax to dynamically apply the current record ID as a filter to the embedded report through a URL query parameter:

src="[POWER BI EMBED URL]&$filter=TASK/WHO_ID eq '{! Contact.Id }'"

I'm pretty sure it worked at some point during testing, but after changes were made to the Power BI report we began receiving this error: "This filter came from a query string parameter that was added to a report URL."

It seems like it's recognizing the filter syntax but not applying the value. We're also testing with a hard-coded ID and getting the same error:

src="[POWER BI EMBED URL]&$filter=TASK/WHO_ID eq '003xxxxxxxxxxxxxxx'"

and

src="[POWER BI EMBED URL]&filter=TASK/WHO_ID eq '003xxxxxxxxxxxxxxx'" (no $)

Is there something we need to do to enable URL query string parameters in this embedded report, or format this value so that it's accepted? There's not much information in the community about this error.

Thanks!