Why is the practice again button not available?

Whenever I finish an exercise, the button on the left hand corner that says "Let's go" or "Next question" briefly turns into "Practice again", but in grey and then turns into a "Done" button. Was there previously an option to practice the skill or shortcut to doing it again?

It would also be helpful right now because each time I click the "Done" button it reloads my page, and when you're at the bottom of a long unit it's quite annoying to have to scroll down on a slow computer. I can't remember if it used to do that.

Just some questions I had haha

-Xiyu