I'm new to responsive projects, so trying to figure this out. I've watched a lot of YouTube videos, which have been very helpful. However, in those the learner is told to mark fluid boxed as "Optional" that they don't want to appear in mobile screens to help with content...and to have "Squeeze to row" as the wrap option. I've done all of this, and the fluid box remains. I've even gone through and marked each child and image in the children as optional.
Your fluid boxes will only not appear when there isn't enough room to display them. Try adjusting the percentage of the utmost parent fluid box to select at what percentage screen size you would like these items to disappear.