There is no WebGUI::Operation::Spectre.pm.
Do you by chance mean WebGUI::Operation::Workflow::www_runWorkflow?
Unless I'm missing something...
https://svn.webgui.org/svnweb/plainblack/view/WebGUI/lib/WebGUI/Operation/Spectre.pm
This line has caused problems:
next unless $instance->getWorkflow->get("enabled");
My bad.
Fixed in 7.3.19, and 7.4.0
getAllInstances will now always return valid objects only, the array ref won't contain undef. Instead, it will log instanceIds that return an undef object.