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 following as you can (you can cut and paste this into your topic):
Nextcloud version (eg, 12.0.0):
Operating system and version (eg, Raspbian jessie with pixel):
Apache or nginx version (eg, Apache 2.4.25):
PHP version (eg, 7.0):
Is this the first time you’ve seen this error?:
Consistently coming
Can you reliably replicate it? (If so, please outline steps):
yes
The issue you are facing:
Hi, I have checked on my raspberry pi that whenever i cancel a download the TCP socket keeps waiting on the FIN_WAIT2 state which makes the next download speed to get decreased. Is it a problem with nextcloud to not send a FIN packet to let the TCP know that the socket is no longer needed hence it should be closed.? How we can achieve that.?
The output of your Nextcloud log in Admin > Logging:
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
The output of your Apache/nginx/system log in /var/log/____:
Remember, this information may be requested if it isn’t supplied; for fastest response please provide as much as you can 
Feel free to use a pastebin service, otherwise log files can be indented with 4 spaces on each line to present them in a friendlier way on the forum.