yii2: http caching always return status 200

What steps will reproduce the problem?

use http cache etag

[
                'class' => 'yii\filters\HttpCache',
                'only' => ['show', 'pdf', 'show-video', 'show-doc'],
                'etagSeed' => function ($action, $params) {
                    $file = UploadedFile::findOne(['id' => \Yii::$app->request->get('id')]);
                    if($file){
                        return serialize([$file->id, $file->created_at]);
                    }
                },
                'sessionCacheLimiter' => 'public',
            ],

What's expected?

Next request should cache return http status 304(not modified)

What do you get instead?

return http status 200 each request

Additional info

Q	A
Yii version	2.0.38
PHP version	7.3
Web Server	Apche 2.4.6 http 1.1
Operating system	Centos 7