Issues posting data - php

Question

I'm trying to insert data to a Wordpress database from a form using the post method. Beofre inserting (code will go where comment is) I'm trying to print the results to screen. When I test my code to collect this data from the form it errors only on one field for some reason. The others post correctly so I'm at a bit of a loss. Below is the code:
global $mydb;
echo '<form name="newProducts" method="post">';
$output = "<div>";
// array of column names
$table_name = $mydb->prefix . '`my-table-names`';
foreach ( $mydb->get_col( "DESC " . $table_name, 0 ) as $column_name ) {
if($column_name!='id'){
$table_name = $mydb->prefix . '`my-table-names`';
$field_name = $column_name;
$getSpecColNameOne = $mydb->get_var($mydb->prepare( "SELECT {$field_name} FROM {$table_name} WHERE id=%d", 0));
$output .= '<div>';
$output .= '<div>' . $getSpecColNameOne . '</div>';
$output .= '<div><input name="' . $column_name . '" type="text" value=""></div>';
$output .= '</div>';
}
}
$output .= '</div>';
echo $output;
$_POST = array_map( 'stripslashes_deep', $_POST );
echo '<div class="btnWrapper">';
echo '<input class="btn border-width-0 btn-text-skin btn-color-jevc btn-square btn-icon-left adduserBtn" type="submit" name="btnSubmit">';
echo '</form>';
if ($_POST) {
$skipKeys = array(
'btnSubmit',
'id',
);
foreach($_POST as $key =>$value){
if(!in_array($key,$skipKeys)){
///insert into db here////////
echo '</br>';
echo"Key:";
print_r ($key);
echo '</br>';
echo"value:";
print_r ($value);
}
}
}
The output I get if I don't fill out column_1 looks like this:
Key:column_1
value:
Key:column_2
value:Input Test 2
Key:column_3
value:Input Test 3
However, if I fill in data into column_1 input field it errors and I get redirected to a 404 page.
column_1 html output looks ok:
<input name="column_1" type="text" value="">
Any ideas appreciated.