We have exactly the same problem and having spent some time with Ruckus support, it appears the issue is related to latency between the cluster members. According to the below T&C's, latency between clusters cannot be more than 8ms:https://support.ruckuswireless.com/software/963-vsz-3-4-ga-software-release-ximg-image/tc
Apart from the above, there is absolutely no documentation that states that your clusters cannot have more than 8ms latency between them.
So the latency is the cause for ElasticSearch going down. So not only is that a problem, but you are unable to restart the ES service yourself. In order to restart ES, you need to contact support. I find this incredible!
Our vSZ-H devices are in geographically separate locations meaning that 8ms latency is near impossible! I have been informed that:
"Please do note that this behavior will change in future
releases where latency will not affect ES services."
No comment on WHEN these future releases will be made available. This means that we have purchased an extra licence that we cannot use.