Yes, it's the latest elasticsearch.
I thought at first that it had something to do with ES not being able to acquire lock on the files on the AWS Elastic Files system. However the AWS documentation says that EFS does support file locks.
So I guess there is some kind of NFS particularity that is bugging things. I also tried mounting the NFS with various options such as noatime,nolock,auto,sec=sys but without any luck.
When I point the data directory to the local file system it works just fine.