The field "password" is missing in eZ\Publish\Core\FieldType\User\Value.

The problem occure where you remove the ezuser field from the /user/update form:

$form->.....->remove('user_account');

Adding the following in eZ\Publish\Core\FieldType\User\Value solve the problem:

    /**
     * Password.
     *
     * @var mixed
     */
    public $password;

This field is used in EzSystems\RepositoryForms\Form\EventSubscriber\UserFieldsSubscriber line 94:

$data->password = $userAccountFieldData->password;

This is why the field should be defined to avoid an exception.