Logstash fails to write in configured Index

[Moritz_Kiesewetter]

Hello guys,
i have the problem, that i want to manage my Index Names by Date.

output {
if [type] == "syslog" {
  elasticsearch {
    hosts => ["XX.XX.XXX.XXX:ZZZZ", "XX.XX.XXX.XXX:ZZZZ", "XX.XX.XXX.XXX:ZZZZ"]
    index => "logstash-%{+YYYY.MM.dd}"

But when i look into my Kibana Discover page, all the logs from logstash come like this:

<189>date Nov 11, 2019 @ 01:00:00.000
@timestamp Nov 11, 2019 @ 11:33:43.801
**t** @version 1
**t** _id ------blackened-------
**t** _index logstash

I don't know why:

1. Logstash Opens up and writes to an Index which is not existant in the config file and is not assigned as IS_WRITE_INDEX
2. If i made any mistakes with the config.

I appreciate all your help! Thanks guys!