I compared the Line visualization between Kibana 7.1.1 and 7.2.1. Based on the same elasticsearch data and the same "Saved Objects" in 7.1.1. and in 7.2.1, the 7.2.1 Line visualization is totaly wrong according to the shown chart / values. See screenshots.
And if you zoom more into the chart in Kibana 7.2.1 then the values come closer to the correct values. Very strange. So at the moment Kibana 7.2.1 is unusable regarding Line visualizations.
I already opened an issue https://github.com/elastic/kibana/issues/42335 because I think this is a serious bug in the Kibana 7.2.1 line visualization.