Unable to receive notifications and announcements on my Apple Watch

Last week everything was working properly. During a workout, the Watch would announce Split notifications (split number and pace) instead of only a chime, it would announce Activity Ring closures instead of only a chime, and it would chime for new notifications (Messages messages, Facebook Messenger messages, Google Chat messages, new email received, etc). Now it's suddenly not working and I have not changed anything.

To try fixing this I've gone into the Watch app on my iPhone (where all notifications are correctly enabled) and in the Activity notifications I disabled then re-enabled Allow Notifications and Goal Completions. In the Workout app section I disabled then re-enabled Alerts on Watch. Still, I get only chimes instead of the Siri announcements.

How do I get my Watch back to working the way it was last week with Siri announcing notifications?

[Re-Titled by Moderator]

Original Title: How do I restore Watch notification announcements?