When using the new stack, in a twig view, to create a link to a legacy module you need to use the following syntax:

{{ path( 'ez_legacy', {'module_uri': '/content/advancedsearch/' } ) }}

It would be good to create a new paragraph in the documentation: https://doc.ez.no/display/EZP/Legacy+code+and+features#Legacycodeandfeatures-Legacymodules

To explain that, to describe all the available parameters and link to twigs path() documentation.