Magento 2.2.2 catalogsearch_fulltext Reindex + Elasticsearch

Dedicate Server 16GB RAM 4 Core Processor Centos Magento 2.2.2 Elastiscearch 6.4

I am trying to run reindex from command line ssh putty php bin/magento indexer:reindex catalogsearch_fulltext

I have elasticsearch 6.4 installed and setup in admin and Test Shows Successful

However when I go to run the reindex it takes many hours and eventually the ssh temrminal disconnects and crashes the whole server and all sites on the server. Only way I can access is by rebooting the server. Otherwise it shows nginx 504 gateway timeout for all sites and also WHM and CPANEL

I managed to work through some of the errors showing previously in elasticsearch log but nothing seems to fix this problem and Ive spent 3 weeks on this.