Hm, yeah with these settings above I'm not sure what would be going on. You should be getting a chart with lines connecting the points, but no fill.
What version of the Elastic Stack are you running? I'm not able to reproduce this on the version I'm testing currently 7.1.1... everything renders as expected. Here's what I'm seeing using some of the kibana_sample_data_logs demo data that ships with Kibana.
