Try this
<div class="main-div">
<?php $outs = array(); if( have_rows('main_field') ): $i = 0;
while ( have_rows('main_field') ) : the_row(); ob_start(); $i++; ?>
<div class="question-answer-template">
<p><?php the_sub_field('sub_feild');?></p>
</div>
<?php $outs[] = ob_get_clean(); endwhile;
else :
endif;
$outs = array_reverse($outs);
echo implode($outs);
?>
</div>
Try this!
<div class="main-div">
<?php $outs = array(); if( have_rows('main_field') ): $i = 0;
while ( have_rows('main_field') ) : the_row(); ob_start(); $i++; ?>
<div class="question-answer-template">
<?php the_sub_field('sub_feild');?>
</div>
<?php $outs[] = ob_get_clean(); endwhile;
else :
endif;
$outs = array_reverse($outs);
echo implode($outs);
?>
</div>