If you did no major change in the server environment and if after a2ensite domain.tld.conf you cannot restart the apache service, this should solve it:

1. Check for syntax errors in one of the Vhost files (this is most probably it).
2. Make sure you have an extra empty row in the end of each Vhost file.

If you did no major change in the server environment and if after a2ensite domain.tld.conf you cannot restart the apache service, this should solve it:

1. Check for syntax errors in one of the Vhost files (this is most probably it).
2. Make sure you have an extra empty row in the end of each Vhost file.

Answer regarding question update:

To solve the syntax error described in the question update above:

a2dissite domain.tld

Note that "domain.tld" deals with the old website you no longer have and to which a symlink stayed in sites-enabled.