Apple Watch Alert causes Reboot?

This morning my Apple Watch Series 4 alerted me to a new challenge – something about National Parks.

When I raised my wrist, the watch rebooted.

How do I make the challenge reappear so I can ‘get after it’?

Thank you,

You see the challenge on your iPhone -> Activity app. Just log a run/hike with 3 miles tomorrow and you will get the “price”.