doesn’t seem to populate with the new entry and return an error that the Note cannot be blank even though there is an entry on the web page and in the Yii::$app->request->post(), yet he $modelsNotes never seems to reflect that.
Calling Model::loadMultiple() subjects each load to $model->setAttributes(), the first thing I’d check is that the data you’re attempting to populate into the models are all valid / safe attributes set in your Model. At the very least you should also see what the return value of Model::loadMultiple(); it should be returning a boolean on whether or not at least one model got populated.