APCu：无法在无效迭代器上调用key()问题求助

我在DDEV（Docker）开发环境中维护旧版本的ILIAS 5.4（一款PHP开发的学习管理系统LMS），运行环境如下：

• GNU/Linux Debian 10 Buster
• PHP 7.3
• MariaDB 10.3

目前遇到APCUIterator相关错误：在调用迭代器key()方法的while循环中，报错「Cannot call key() on invalid iterator」。相关代码片段如下：

/**
 * @param bool $complete
 *
 * @return bool
 */
public function flush($complete = false)
{
    if ($complete) {
        return apcu_clear_cache();
    }

    $key_prefix = $this->returnKey('');
    $apcu_iterator = new APCUIterator();
    $apcu_iterator->rewind();
    while ($current_key = $apcu_iterator->key()) {
        // "begins with"
        if (substr($current_key, 0, strlen($key_prefix)) === $key_prefix) {
            $this->delete($current_key);
        }
        $apcu_iterator->next();
    }
    return true;
}

在容器中用以下极简代码可复现错误：

<?php
$iterator = new APCUIterator();
$iterator->key();
# Nothing else matters

我猜测容器中缺少依赖或配置存在问题，恳请提供排查建议。

容器内APC配置信息（执行ddev php -i | grep -i apc输出）： #

/etc/php/7.3/cli/conf.d/20-apcu.ini,
/etc/php/7.3/cli/conf.d/25-apcu_bc.ini,
/etc/php/7.3/cli/conf.d/enableapcu.ini,
apc
APC Compatibility => 1.0.5
apcu
APCu Support => Enabled
APCu Debugging => Disabled
apc.coredump_unmap => Off => Off
apc.enable_cli => On => On
apc.enabled => On => On
apc.entries_hint => 4096 => 4096
apc.gc_ttl => 3600 => 3600
apc.mmap_file_mask => no value => no value
apc.preload_path => no value => no value
apc.serializer => php => php
apc.shm_segments => 1 => 1
apc.shm_size => 32M => 32M
apc.slam_defense => Off => Off
apc.smart => 0 => 0
apc.ttl => 0 => 0
apc.use_request_time => Off => Off
igbinary APCu serializer ABI => 0

原生staging系统（非Docker，Debian+Apache）的APC配置信息： #

/etc/php/7.3/cli/conf.d/20-apcu.ini,
apcu
APCu Support => Disabled
APCu Debugging => Disabled
apc.coredump_unmap => Off => Off
apc.enable_cli => Off => Off
apc.enabled => On => On
apc.entries_hint => 4096 => 4096
apc.gc_ttl => 3600 => 3600
apc.mmap_file_mask => no value => no value
apc.preload_path => no value => no value
apc.serializer => php => php
apc.shm_segments => 1 => 1
apc.shm_size => 32M => 32M
apc.slam_defense => Off => Off
apc.smart => 0 => 0
apc.ttl => 0 => 0
apc.use_request_time => On => On

内容的提问来源于stack exchange，提问作者mrkskwsnck