Inconsistent ascending/descending ordering

[wbjrpub]

Kibana version:
6.4.0
(we've had this issue with ES1.7 / Kibana4 and were hoping an upgrade would have solved this).

Elasticsearch version:
6.4.0

Server OS version:
Centos 7.3.1611

Browser version:
Chrome 68.0.3440.106

Browser OS version:
MacOS 10.12.6

Original install method (e.g. download page, yum, from source, etc.):
yum

Describe the bug:
We've been using a line visualization with Terms aggregation on a keyword field, and splitting the series using another keyword field.
We are getting lines that zigzag (see screenshot).
The zigzags doesn't always happen, it is data dependent.
We don't see zigzags if we change the first aggregation to Descending.
We don't see zigzags if we change this from a Terms aggregation to a Date Histogram.

Steps to reproduce:
It will take some time to extract the data from our system as an example,
please let me know if you would need this (and in what format - bulk upload?).

Expected behaviour:
No zigzags.

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:
Original issue on Kibana forum

[timroes]

This looks like an duplicate of #17532