Can you specify which logstash version you are using, and can you share your configuration?
It may depends on the mode you set: it may be tail or read. it defaults to tail, which means it listens on your file and it waits for default 1 hour before closing it and stopping waiting for new lines.
You may have to change this parameter fro 1 hour to 1 second if you know you have reached the EOF yet:
file {
close_older=> "1 second"
}
Let me know if that works!
Docs here: https://www.elastic.co/guide/en/logstash/current/plugins-inputs-file.html#plugins-inputs-file-close_older