Which version of Krita are you using?
Even if layers are “animated” it seems you don’t have keyframes 
The first thing is to create keyframes.
In timeline, right-click and then “Create blank frames”
On each frame, you’ve to draw the content that will define animation
At the end, in menu File, you have to render animation and choose WebM format
Here’s complete animation tutorial for beginners:
Grum999