"Unknown elastic error response" when group by size exceeds a certain value

I assume this to be a Grafana configuration issue.
I am using Elastic Search 7.3 and Grafana 6.3.3 (and Kibana 7.3)
I am collecting periodic data from ‘ps -aux’ and graphing the VSZ and RSS for each reported command over time.
When I build a TSV in Kibana I can group, I can group by the top 50 or more and get a very busy chart :slight_smile:
However, when I do the same in Grafana, if I go over some arbitrary ‘group by’ threshold (Top 12 in this particular case) I get nor graph and a red ‘!’ bang in the upper left corner that expands to “Unknown elastic error response”
12 is not a magic number. I do this for several hosts and some size limits are 15 some are 20 but I can never reach the 50 mark.
Is there some config I need to do to Grafana to increase this size?