@pretoescuro @hphillip @grsham Turns out OpenLayers6 Geometry constructors now require a coordinate array even if it’s empty. I’ll commit a fix in the next release.
For a quick fix, edit line 947 in /usr/share/dump1090-fa/html/script.js and add an empty array.
var geom = new ol.geom.LineString([]);
Let me know if this fixes your issues.