Posts stuck together

I’m completely confused why my posts’ excerpts are stuck together. Here’s an image.

https://www.elmuseo.org/sites/default/files/postsstucktogethe.PNG

Essentially, this page has a page template that allows the excerpts of posts with a certain category to automatically appear in a grey box. What confuses me is how the order of the posts is picked and why it sometimes sticks two post excerpts together.

Thanks in advance.