Error messages and no idea

I am running OC on a Ubuntu Server. A lot of syncing is working very well but sometimes (I did not find out when) I am receiving a error message. It seams a double change on two different devices might be the issue. Even if changes are not on same file.

Error message is shown in windows tray.
For Android I am using foldersync

Any ideas where I should search for a solution?

In nginx log I found this one but I am not sure what to do

2017/02/05 21:55:47 [error] 42846#42846: *88489 FastCGI sent in stderr: "PHP message: {"reqId":"xNIp0If3QFK\/UZUSIlBG","remoteAddr":"","app":"PHP","message":"chmod(): Permission denied at \/var\/www\/owncloud\/lib\/private\/Log\/Owncloud.php#114","level":3,"time":"2017-02-05T21:55:47+01:00","method":"PUT","url":"\/owncloud\/remote.php\/webdav\/DCIM\/Camera\/20161101_152305.jpg","user":"android"}" while reading upstream, client:, server:, request: "PUT /owncloud/remote.php/webdav/DCIM/Camera/20161101_152305.jpg HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.0-fpm.sock:", host: ""

Please fill out the issue template shown when creating a new thread. Currently all basic information about your environment (oC version, PHP version etc.) are missing.

The mentioned issue template is not shown for fun and is asking you all infos which are needed to help here.

Hello and sorry for that. It did not display because I startetd writting before choosing a category so I was not aware about your issue form. Maybe some good idea to give a hint for choosing category first.