rows in Bootstrap grid don't line up - html

Question

Just trying to make a second row of col-md-6s (I copied the "row" div and pasted it within the container div) but I can't seem to figure out why its not perfectly lined up.
The last two lines of HTML code reflect the beginning of the second row.
.btn-group-vertical{
border: 2px solid black;
border-radius: 10px;
}
.col-md-6 {
display: flex;
justify-content: center;
flex-wrap: wrap;
}
#prod_view {
height: 100%;
background-color: lightcoral;
display: flex;
justify-content: flex-start;
border: solid;
border-radius: 10px;
}
.col-md-6 > div:last-child {
width: 50%;
}
.boxclass {
height: 95%;
width: 50%;
}
<div class="container">
<div class="row">
<div class="col-md-6" style="background-color: lightcyan">
<div class="btn-group-vertical btn-group-lg">
<button type="button" class="btn btn-primary">Quick Select</button>
<button type="button" class="btn btn-primary">Show in Depth</button>
<button type="button" class="btn btn-primary">Delete Product</button>
</div>
<div>
<div id="prod_view">
<div class="boxclass" >
<img alt="product" class="img-rounded" src="../Images/math.jpg" style="max-height: 100%; max-width: 100%;">
</div>
<div class="boxclass">some cool blocks all stacked up n shtufff</div>
</div>
</div>
</div>
<div class="col-md-6" style="background-color: lightgray">
<div class="btn-group-vertical btn-group-lg">
<button type="button" class="btn btn-primary">Quick Select</button>
<button type="button" class="btn btn-primary">Show in Depth</button>
<button type="button" class="btn btn-primary">Delete Product</button>
</div>
<div>
<div id="prod_view">
<div class="boxclass"></div>
<div class="boxclass"></div>
</div>
</div>
</div>
<div class="row">
<div class="col-md-6" style="background-color: lightcyan">

Answer 1

Works fine when the .row is closed properly...
http://www.codeply.com/go/OCsEsFb2Lr
<div class="container">
<div class="row">
<div class="col-md-6" style="background-color: lightcyan">
</div>
<div class="col-md-6" style="background-color: lightgray">
</div>
</div>
<div class="row">
<div class="col-md-6" style="background-color: lightcyan">
</div>
<div class="col-md-6" style="background-color: lightgray">
</div>
</div>
</div>