I had the following problems with the bestsellers displayed in the sideboxes:
- In Configuration -> Maximum Values -> Best Sellers for Box I had to put in 11 to display 10 bestseller.
- The number 1 bestseller was never displayed. It started with the second best selling item.

I fixed it by modifying includes/templates/bootstrap/sideboxes/tpl_best_sellers.php.
Line 19
Code:
for ($i = 1, $j = count($bestsellers_list); $i<$j; $i++) {
should be
Code:
for ($i = 0, $j = count($bestsellers_list); $i<$j; $i++) {
Line 22
Code:
$i . '. ' .
should be
Code:
$i+1 . '. ' .
Somebody check please.