app/node_modules/ng-zorro-antd/form/style/patch.less

// Since zorro's form-item-margin-bottom doesn't currently animate, we need to fix some of the heights.
.@{form-item-prefix-cls}{
  &-explain-connected {
    height: 0;
  }

  &-with-help {
    margin-bottom: 0;
  }

  &-with-help &-explain {
    min-height: @form-item-margin-bottom;
  }
}