Comment 2 for bug 1627817

AFAICT the Knot LPE fails to support elliptical arc path commands used in Inkscape 0.91 and later to originally represent circle/ellipse shapes converted to path (rev >= 12677):
https://www.w3.org/TR/SVG11/paths.html#PathDataEllipticalArcCommands

The number of nodes (as displayed with the node tool) does not really matter - it's sufficient to trigger a rewrite of the path data in the node tool context to convert the elliptical arcs to cubic bézier curves (without inserting additional nodes). The Knot path effect then works as expected with cubic bezier curves.

Workaround based on the reporter's 'steps to reproduce':
1) draw overlapping circles
2) combine (Ctrl+K)
3) convert elliptical arcs into cubic bezier curves
[ for example: switch to node tool ('N'), select all ('Ctrl+A') - or any amount of nodes >= 1 - and nudge the selection with the cursor keys (e.g. one step up and one back down again) ]
4) apply Knot Effect to the combined path
5) adjust parameters as needed

Reproduced with lp:inkscape >= 12677 and lp:inkscape/0.92.x r15091 (on OS X 10.7.5).