Hi there! Thanks for that suggestion, Noda!
Thanks to you, I figured out the problem. It’s Jetpack. Without Jetpack, the white space instantly disappears.
The problem is (aside from the fact that Jetpack has a lot of really helpful features which made me really sad to deactivate it), after I deact the plugin, this is what it said on my dashboard:
The Jetpack plugin is necessary to use some of this theme’s features, including: Content Option (no specific module needed). Please activate Jetpack by WordPress.com. Activate
So if Jetpack is actually an important part of this theme, how come it messes up the homepage?
And actually, without Jetpack, all the posts show up as full posts and not excerpts. There’s no option to enable just excerpts in the theme too. Only Jetpack allowed me to do it. Now I’m manually adding excerpts to each one of my posts. sigh