I have an issue with connecting second cluster to Elasticsearch. I changed dynamic mappings and added best_compression to the settings, but now I get an error every time I try to connect new beats to it.
If I leave the field from the automatically created index pattern:
The problem at some point you deleted the alias and then started one of the metricbeat is it started to write to metricbeat-7.17.1 which the write alias did not exist and so it started writing to a regular index named metricbeat-7.17.1
So to fix...
Stop all your metricbeats.
Clean up / delete the bad index DELETE metricbeat-7.17.1 from the Kibana - Dev Console and YES you will lose data