I too had this problem of blank space showing between sections, and it look quite a few things to resolve it. As the above user mentioned, setting your row height to auto can help.
In addition, I found that when you right click on each section and go to Section Properties... the Size tab had a fixed height for my sections. Once that was changed to auto as well, the issue was resolved. Keep in mind that if you set a section to auto and then manually adjust it later, it will go back to a fixed size. So, I advise changing the height to auto last.
If there is still white space after that, remove all padding from every cell, section, and control (set to 0 not auto.) Sometimes, even margins can have similar effects on your form; usually I try to only have margins at the bottom of controls rather than on sections or cells. All of these changes removed the white space between hidden sections.
Hopefully that helps!