Hi @epstein
Lets try a few things.
1. Turn on DEBUG_MODE in your wp-config.php file. This will show any PHP errors
2. What version of ACF are you using?
3. Try debugging the value like so:
<?php
$banners = get_field('bottom_banners');
echo '<pre>';
print_r( $banners );
echo '</pre>';
die; ?>
4. Is this code in the footer.php? If so, is the $post correct for ACF to load from the correct post/page?