It seems your nodes are unable to store the system index (.security index). Try to change your master node role as data_content by adding data_content role in node_roles of your nodes YML file.
Refer the below post for more detail-
After changing the role UUID of the node will change so in such case for existing cluster you need to kill all elastic node process then change the node role and restart your other node which results your cluster up and after that you'll not face this issue.
incase of any doubt share your YML settings or if it resolves let us know for the same.
Good luck!