Hello @ale_sabat
From the first screenshot i see [NO_MASTER], this would be a configuration, network, service issue.
I personal would start to make sure all services ( ES, Mongo & Graylog) are running without errors or warnings.
If all node/service are fine then I would check configruations on all Graylog config file to ensure they are correct
And last, check Firewalls/ SELinux/AppArmor for blocking network connecions.
If all the above is good, then dig in to the log files Elasticsearch/Graylog and MongoDb. and post your finding here if you can.
Here are some post you can check out