Drilldown Configurations not showing (don't work) in "Alert Manager" app

[woodcock]

We deploying Alert Manager with a new client.

Most of my alerts have a "DRILLDOWN_URL" field which contains context-specific SPL.
I am trying to configure this to be a 1-click operation to run using "Drilldown Actions" but these do not work:

_key	name	label	url
6169aad5005c277d3b3788d5	Splunk search to show contributing events for this instance of this alert	Contributing Events	https://localhost:8000/en-US/app/alert_manager/search?q=$DRILLDOWN_SPL|u$
6169af6f005c277d3b3788d6	Splunk search to show contributing events for this instance of this alert	Contributing_Events_2	https://localhost:8000/en-US/app/alert_manager/search?q=$DRILLDOWN_SPL$

I still get no drilldowns defined in the investigation screen.