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Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
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, 12.0.2): 12.0.3
Operating system and version (eg, Ubuntu 17.04): Debian 9
Apache or nginx version (eg, Apache 2.4.25):
PHP version (eg, 7.1):
The issue you are facing:
When downloading a file within a shared Folder the download ico arrow changes to a spinning wheel (Icon-loading-small) and stays rotating but the download happened.
This behaviour is Independent from Browser or client oS version
Nothing Special in the logs
Is this the first time you’ve seen this error? (Y/N): N
Steps to replicate it:
The output of your Nextcloud log in Admin > Logging:
Debug core Scss is disabled for /var/www/nextcloud/core/css/share.scss, ignoring 2018-05-08T14:08:49+0200
Debug core Scss is disabled for /var/www/nextcloud/core/css/server.scss, ignoring
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
PASTE HERE
The output of your Apache/nginx/system log in /var/log/____:
PASTE HERE