Email editor in the docked not change to new UI after I run Test new lightning email compose

I switched to the new Lightning Email Compose in my Sandbox, but I noticed that only the Email Compose in the Case Feed has been updated to the new UI. The docked email editor remains unchanged and still uses the old UI.

However, when I tested it in another org (Developer Trial), both the docked email editor and Case Feed email editor were updated to the new UI.

Is there a difference between Sandbox and Production environments when applying new features?

Thank you for your help!