Hi Francesco,
Can you check your Elasticsearch cluster for any issues. One problem that can happen is that disk drives get above a high water mark and that makes indices turn to read-only mode. If you have monitoring enabled and if that's working, that would be a good place to check.
If Kibana monitoring isn't enabled or isn't working because of those degraded plugins, you might have to use curl commands something like this (you may have to add -u username:password);
curl -XGET "https://localhost:9200/_cluster/health" -H "kbn-xsrf: reporting"
and
curl -XGET "https://localhost:9200/_nodes/stats" -H "kbn-xsrf: reporting"
If those don't reveal any problems, it looks like there might be a problem with a rule. It could be a built-in rule or a custom rule. If you have rules you could try disabling them and see if the issue clears up.
Please let us know if you find the problem.
Regards,
Lee