Pattern along Path: when there is a circle in the selection that is not the topmost object, the circle is enlarged and moved away
According to the extension logic, the user is asking the extension to tile the pattern along the circumference of a circle.
When I try this, the second circle just gets removed. (update: it's only moved. Out of the viewport. And enlarged.)
Inkscape should either work with circles as target of the PaP extension, or it should at least give an error message as to why it does not work.