Monthly Challenge changed during the same day?

Greetings,

First of all, if that matters, I have 2 Apple Watches.

Now to the question at hand: This morning, when I checked the monthly challenge for March, it was to burn xxx calories during the month. First time I got that one, no issues with that.

This evening, for my workout session, I switched to my other Apple Watch (it's a Series 2, while my daily is a Series 3) and did my workout. At the end I got a notification on the Watch announcing my March challenge, and instead of saying to burn xxx calories during the month, it was earning xxx minutes during the month.

Why, all of a sudden, the monthly challenge, for March has changed during the same day? Is it because of having 2 Apple Watch synced with the phone and both have a life on their own? Is it something else?

Thank you for clarifying that 🙂

Patrick