nginx: [warn] conflicting server name "dataanalyst.gr" on 0.0.0.0:80, ignored
nginx: [warn] conflicting server name "www.dataanalyst.gr" on 0.0.0.0:80, ignored
nginx: [warn] conflicting server name "dataanalyst.gr" on [::]:80, ignored
nginx: [warn] conflicting server name "www.dataanalyst.gr" on [::]:80, ignored
You should read the config files in /etc/nginx/sites-enabled and see how many server blocks there are, and what are the listen and server_name directives for each of them.
Inside the /ect/nginx/sites-enabled there are two files, the dataanalyst.gr and the default. Both listening to the same ports and both having server_name dataanalyst.gr www.dataanalyst.gr;.