Thank you for your help. I added the setRelation and the loading hang has stopped.
However, there are no records found. If I comment out the setRelation then records are found.
public function notes($id)
    {
        $crud = $this->_getGroceryCrudEnterprise();
        $crud->setSkin('bootstrap-v4');
        $crud->setTable('notes');
        $crud->setSubject('Note', 'Notes');
        $crud->columns(['client_id','title','date','body']);
        $crud->where(['notes.client_id' => $id]);
        
        $crud->displayAs('client_id','Account');
        $crud->displayAs('date','Date of Note');
        $crud->unsetFields(['created_at', 'updated_at']);
        $crud->setTexteditor(['body', 'full_text']);
       
        $crud->fieldType('title', 'dropdown_search', [
            'Progress' => 'Progress',
            'General' => 'General'
        ]);
        
        $crud->setRelation('client_id', 'clients', '{first_name} {middle_name} {last_name}', ['id' => $id]);
        $this->userId = $id;
        
        $crud->callbackAddForm(function ($data) {
            $data['client_id'] = $this->userId;
            return $data;
        });
                        
        $output = $crud->render();
        $data['title'] = 'Client:';
        $data['client'] = $this->client_model->get_clients($id);
        $client_name =  $data['client']['first_name'] . ' ' . 
                        $data['client']['middle_name'] . ' ' . 
                        $data['client']['last_name'];
         
        $this->_crud_output($output,$client_name);
        
        
    }