What type of objects are not supported in a Fluid Box?
Rollover Captions, Rollover Images, and Rollover Slidelets are not supported in a Fluid Box.
The Suggest Fluid Boxes workflow also ignores grouped objects.
For example, let there be a group of three objects in a slide. Also, insert a smart shape as a button and assign an advanced action to the button that applies an effect to the group.
If you click Suggest Fluid Box, you can see that the Fluid Box ignores the group. So, a group of objects can never be a part of a Fluid Box.