Why does the Class 'CIBlockSection' not found (0) error occur?

Question

1C-Bitrix

I can not understand, I did a system restore through backup and I get an error

Class 'CIBlockSection' not found (0)
/home/bitrix/www/local/components/fiss/top.menu/component.php:39

It is possible that this class does not exist, but I do not understand where to get it? and what to do in this case and where it should lie.
I decided to look at the code and there in the file bitrix/modules/iblock/iblock.php

"CIBlockSection" => "classes/".$DBType."/iblocksection.php",

But I don’t even see the classes directory in the project