It looks like your index was created with a new version of Beats that is implementing the ECS (Elastic Common Schema), but that the Logstash output isn't quite in the same shape 
ECS has a host.name field, which corresponds to the host name being output from Logstash. By adding a Mutate filter with a rename directive, you can move the host field to host.name with the field-reference syntax as below to align with the schema that you already have in Elasticsearch:
filter {
mutate {
rename {
"[host]" => "[host][name]"
}
}
}