The issue stems from the fact that scene arrays are not cleared when rendering is done. This was not really an issue before the introduction of the ownership system (rB429afe0c626a) as the id_map would recreate scene data arrays based on their new content. However, now that the id_maps do not have access to the scene data anymore the arrays are never created.

Another related issue is that the BlenderSync instance is never freed when the persistent data option is activated.

To fix this, we delete nodes created by the id_maps in their destructors, and delete the BlenderSync instance before creating a new one, so the id_maps destructors are actually called.