(and https://github.com/elastic/elasticsearch/blob/master/x-pack/plugin/core/src/main/resources/monitoring-es-mb.json#L742 which derives from fields.yml) maps elasticsearch.node.stats.os.cgroup.memory.limit.bytes as long, but according to https://www.elastic.co/guide/en/elasticsearch/reference/current/cluster-nodes-stats.html it's a string value.

Normally the implicit conversion is fine, but in some cases (forum example) it will return max which causes an error at indexing time due to the long mapping in the template.