The first two Google hits for elasticsearch glusterfs lead to two serious-looking open GlusterFS issues that Elasticsearch triggers:
https://bugzilla.redhat.com/show_bug.cgi?id=1390050
https://bugzilla.redhat.com/show_bug.cgi?id=1379568
This may be one of them, or may be something else, but it seems worth rethinking your setup.
I don't think so. Both of the times I quoted are in UTC (note the trailing Z) and differ by 28 seconds, so it seems unlikely to be a timezone issue.