After every Restart of Jenkins the ftp-servers are lost.
For your information, all publish-over-ftp component type JENKINS issues related to the Publish Over FTP plugin have been transferred to Github: https://github.com/jenkinsci/publish-over-ftp-plugin/issues
Here is the direct link to this issue in Github: https://github.com/jenkinsci/publish-over-ftp-plugin/issues/48
And here is the link to a search for related issues: https://github.com/jenkinsci/publish-over-ftp-plugin/issues?q=%22JENKINS-18336%22
(Note: this is an automated bulk comment)