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Sorry to hear you’re facing problems 
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In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 18.0.2): 19.0.2
Operating system and version (eg, Ubuntu 20.04): Ubuntu 18.04 (But in a Docker container)
Apache or nginx version (eg, Apache 2.4.25): nginx/1.19.2 (Docker), nginx/1.14.0 (Host)
PHP version (eg, 7.1): PHP 7.4.9
The issue you are facing:
I found this issue after I upgrade my Nextcloud instance from v18.0.2 to v19.0.2.
I mounted a AWS S3 bucket onto /s3 as an external storage, and there is a folder /s3/photos containing about 200 subdirectories. After I upgraded the Nextcloud, I can’t access to this folder any more. Everytime I try to list the subdirectories in it via WebDav (/remote.php/dav), I got a 504 Gateway Timeout error.
This issue doen’t occur on other folders like /s3/another/folder, and I can even still access to its subfolders by directly using the path (e.g.: /s3/photos/2019).
I tried to change the nginx configuration by adding:
fastcgi_ buffer s 512 64K;
client_max_body_size 10G;
But it didn’t work.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
- Install Docker via this docker-compose.yml
- Mount a S3 external storage
- Create about 200 directories(or files) in it.
The output of your Nextcloud log in Admin > Logging:
Couldn't find related records.
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'memcache.local' => '\\OC\\Memcache\\APCu',
'apps_paths' =>
array (
0 =>
array (
'path' => '/var/www/html/apps',
'url' => '/apps',
'writable' => false,
),
1 =>
array (
'path' => '/var/www/html/custom_apps',
'url' => '/custom_apps',
'writable' => true,
),
),
'instanceid' => 'ID',
'passwordsalt' => 'SALT',
'secret' => 'SECRET',
'trusted_domains' =>
array (
0 => 'localhost:8001',
1 => 'example.com',
),
'datadirectory' => '/var/www/html/data',
'dbtype' => 'mysql',
'version' => '19.0.2.2',
'overwritehost' => 'example.com',
'overwriteprotocol' => 'https',
'overwrite.cli.url' => 'https://example.com',
'dbname' => 'nextcloud',
'dbhost' => 'db',
'dbport' => '',
'filelocking.enabled' => false,
'dbtableprefix' => 'oc_',
'mysql.utf8mb4' => true,
'dbuser' => 'nextcloud',
'dbpassword' => 'nextcloud',
'installed' => true,
'maintenance' => false,
'loglevel' => 2,
);
The output of your Apache/nginx/system log in /var/log/____:
52.229.162.3 - - [06/Sep/2020:23:34:59 +0800] "PROPFIND /remote.php/dav/files/admin/s3/photos HTTP/1.1" 499 0 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36"
2020/09/06 23:34:59 [error] 11251#11251: *7645 upstream timed out (110: Connection timed out) while reading response header from upstream, client: xxx.xx.xx.xx, server: example.com, request: "PROPFIND /remote.php/dav/files/admin/s3/photos HTTP/1.1", upstream: "http://127.0.0.1:8001/remote.php/dav/files/admin/s3/photos", host: "example.com"
