Comment # 1 on bug 1144361 from Luiz Fernando Silva

My first guess is that this behavior is part of some "check for updates at
start" type of setting, but to my surprise I could not find anything in
LibreOffice's settings to disable this.
There used to be a setting for this in LibreOffice 5 [Tools - Options -
LibreOffice - Online Update], but not anymore on 6, at least not in the version
available in Tumbleweed.

I also tried poking around in LibreOffice's advanced settings looking for any
entries for ftp://ftp.libreoffice.org, but couldn't find anything.

If this is not a "check for updates at start" setting, I wonder why is
LibreOffice trying to resolve the above URL.

I started a FTP server on my machine, which due to the alias I added to
/etc/hosts, would receive the connection attempts done by LibreOffice. No
traffic was observed, all that LibreOffice is doing during startup is name
resolution, no actual FTP connection is made whatsoever.