Bootstrap col-md-6 added by itself

Question

As you can see in the img shown below of my website : http://chorale-universitaire-nancy.com/concerts.php

It's weird as there are 6 rows missing, and no reason why! Can someone help me and tell me what am I missing? The image shows exactly what I mean, and you have the website where you can "Inspect Element". Sorry for my English.

Answer 1

It is not missing, one of your images are higher than another! which is causing the white-space you see, the best way to fix this is to add a div with class row around each two col-md-6 divs:

<div class="row">
   <div class="col-md-6">...</div>
   <div class="col-md-6">...</div>
</div>

Answer 2

It is a problem with CSS floats. To fix it you can use Flexbox. Just add

display: flex;
flex-wrap: wrap; 

to the row div which is encompassing all the images.