When the PIR sensor is triggered, it sends the notification multiple times and the automation will turn back on when the PIR sensor is triggered on the second time even though it is only seconds apart.
That means, I would be bombarded by the notifications when someone is moving around in the backyard.
I may be captain obvious here but automation.speaker__backyard isn’t turning off/on your automation. Just for the giggles, can your rename your alias to something without dashes or underscores - say like ‘giggles’. Then your entity_id would be automation.giggles. Try that.