Just a short info for everyone facing the same issue before we can fix this:
This is caused by a failed update of the elasticsearch. There are probably a lot of Zammad scheduler tasks that try to update the elasticsearch but can’t due to the incompatibility resulting from the error.
So here is how you can resolve the issue (commands may vary depending on your OS and installation source):
- Stop the whole Zammad application (e.g.
systemctl stop zammad) - Delete all failed jobs by running
zammad run rails r "Delayed::Job.delete_all("attempts > 1") - Stop your elasticsearch (e.g
systemctl stop elasticsearch) - Delete your old elasticsearch indexes (e.g.
rm -rf /var/lib/elasticsearch/nodes/0/indices/*) - Install the elasticsearch
ingest-attachmentplugin (e.g.sudo /usr/share/elasticsearch/bin/elasticsearch-plugin install mapper-attachments) - Start your elasticsearch again (e.g.
systemctl start elasticsearch) - Rebuild your elasticsearch index by running
zammad run rake searchindex:rebuild(This may take a while depending on the amount of data in your Zammad) - Start the whole Zammad application again (e.g.
systemctl stop zammad)
After that your Zammad should be back on track and run smooth as it should 
We are working on resolving this.