bbPress.org

Line 4255 of your theme Pixiehuge has

#bbpress-forums li.bbp-body ul.forum li {
	height: 100%;
	display: flex;
	display: -webkit-flex;
	flex-direction: column;
	-webkit-flex-direction: column;
	justify-content: center;
	-webkit-justify-content: center;
}

The height : 100% is the issue

You need to put

#bbpress-forums li.bbp-body ul.forum li {
	height: auto;
}

or

#bbpress-forums li.bbp-body ul.forum li {
	height: auto !important;
}

(Try without the !important first)

into your theme’s custom css, or the custom css part of my bbp style pack plugin