Web interface shows file size correctly, but downloading fails with empty file

Hi,

I’m running a nextcloud on my raspberry PI:
NextCloudPi version v1.15.3
NextCloudPi image NextCloudPi_07-21-19
distribution Raspbian GNU/Linux 10 \n \l

The issue I’m facing ist that there are file sizes are displayed correctly in the WebInterface, but if I try to download them, they are empty: The download dialog shows 0 byte and the file stored locally has a size of 0 bytes.
If I re-upload the files it seems to solve the problem for some time, but then the file empty again when I try to download it.

Also the desktop client has error messages stating something like: “The file is empty though the server said it should be 10MB”

I could not find a solution in the forum.
Maybe someone can give me a hint what I could do to solve the problem?

Regards
Klaus

Apache error log

 sudo cat /var/log/apache2/error.log
[Mon Oct 14 00:00:16.781343 2019] [ssl:warn] [pid 771:tid 1995629072] AH01909: localhost:4443:0 server certificate does NOT include an ID which                                matches the server name
[Mon Oct 14 00:00:16.783937 2019] [mpm_event:notice] [pid 771:tid 1995629072] AH00489: Apache/2.4.38 (Raspbian) OpenSSL/1.1.1c configured -- res                               uming normal operations
[Mon Oct 14 00:00:16.783999 2019] [core:notice] [pid 771:tid 1995629072] AH00094: Command line: '/usr/sbin/apache2'
[Mon Oct 14 04:00:01.186544 2019] [mpm_event:notice] [pid 771:tid 1995629072] AH00491: caught SIGTERM, shutting down
[Mon Oct 14 04:00:57.027907 2019] [ssl:warn] [pid 552:tid 1995411984] AH01909: localhost:4443:0 server certificate does NOT include an ID which                                matches the server name
[Mon Oct 14 04:00:57.079926 2019] [ssl:warn] [pid 726:tid 1995411984] AH01909: localhost:4443:0 server certificate does NOT include an ID which                                matches the server name
[Mon Oct 14 04:00:57.085707 2019] [mpm_event:notice] [pid 726:tid 1995411984] AH00489: Apache/2.4.38 (Raspbian) OpenSSL/1.1.1c configured -- res                               uming normal operations
[Mon Oct 14 04:00:57.085845 2019] [core:notice] [pid 726:tid 1995411984] AH00094: Command line: '/usr/sbin/apache2'
[Mon Oct 14 19:54:46.301458 2019] [proxy_fcgi:error] [pid 731:tid 1849259040] [client 192.168.2.22:51226] AH01071: Got error 'PHP message: PHP N                               otice:  Undefined index: app in /var/www/ncp-web/index.php on line 238PHP message: PHP Notice:  Undefined index: app in /var/www/ncp-web/index.p                               hp on line 244'

config.php

$CONFIG = array (
  'passwordsalt' => 
  'secret' => 
  'trusted_domains' =>
  array (
[...]
  ),
  'datadirectory' => '/media/USBdrive/ncdata',
  'dbtype' => 'mysql',
  'version' => '16.0.3.0',
  'overwrite.cli.url' => xxxxxxxxxxx,
  'dbname' => 'nextcloud',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'ncadmin',
  'dbpassword' => 'xxxxxxxx',
  'installed' => true,
  'instanceid' => 'oclaqn5ofjmm',
  'memcache.local' => '\\OC\\Memcache\\Redis',
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'redis' =>
  array (
    'host' => '/var/run/redis/redis.sock',
    'port' => 0,
    'timeout' => 0.0,
    'password' => 'xxxxxxxxxxxxxxxxx',
  ),
  'tempdirectory' => '/media/USBdrive/ncdata/tmp',
  'mail_smtpmode' => 'sendmail',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_from_address' => 'admin',
  'mail_domain' => 'ownyourbits.com',
  'preview_max_x' => '2048',
  'preview_max_y' => '2048',
  'jpeg_quality' => '60',
  'overwriteprotocol' => 'https',
  'maintenance' => false,
  'logfile' => '/media/USBdrive/ncdata/nextcloud.log',
  'loglevel' => '2',
  'log_type' => 'file',
);

Some days later, after this problem occured, my SD card got damaged. I cannot reboot the raspberry pi. Maybe the empty file problem was an early indication for sd card problems?
However, I cannot investigate this further, since I have to reinstall Nextcloud.