Typically the issue is that if you are using a flexible layout with a scale set on the height value, this may collapse down to 0 pixels if there's not an explicit height on some parent element. The two solutions are:
- Uncheck the height scale in the scene/layout editor so it does not use flexible layout on height
- Introduce a container that has a height specified
There's more info in the " Setting a CSS Class or Minimum Height on a Responsive Document" section of this post:
And if you search "wordpress height" you'll find some more solutions as it is a common issue!