An unserialize wrapper that gets rid of "Error at offset" errors.

unserialize_after_fixing.php

<?php

/**
 * This function fixes string lengths before unserializing a value,
 * in case some content was found and replaced, for example.
 *
 * @param  string $str
 * @param  array  $options
 * @return mixed
 */
function unserialize_after_fixing($str, array $options = [])
{
    $str = preg_replace_callback('/s:(\d+):"(.*?)";/s', function ($matches) {
        return 's:' . strlen($matches[2]) . ':"' . $matches[2] . '";';
    }, $str);

    if (version_compare(PHP_VERSION, '7.0.0') >= 0) {
        return unserialize($str, $options);
    }

    return unserialize($str);
}