org.elasticsearch.xpack.monitoring.exporter.ExportException: [.monitoring-es-7-2019.05.09] IndexCreationException[failed to create index [.monitoring-es-7-2019.05.09]]; nested: ValidationException[Validation Failed: 1: this action would add  total shards, but this cluster currently has / maximum shards open;]
Looks like you have to many shards for 1 node.
The best way would be to reduce your Shards. temporary you can incress the 1000 Shards limit, see: https://www.elastic.co/guide/en/elasticsearch/reference/current/allocation-total-shards.html
I recommend to read this Article: https://www.elastic.co/blog/how-many-shards-should-i-have-in-my-elasticsearch-cluster
What is the output of:
GET / GET /_cat/nodes?v GET /_cat/health?v GET /_cat/indices?v
If some outputs are too big, please share them on gist.github.com and link them here.