Got it: wasn't checking atom body

while (!lv2_atom_sequence_is_end(
                               &self->control->body, self->control->atom.size, ev)) {
                        // If the event is an atom:Blank object
                        if (ev->body.type == self->uris.atom_Blank) {
                                const LV2_Atom_Object* obj = (const LV2_Atom_Object*)&ev->body;
                                if (obj->body.otype == self->uris.ui_On) {