Every hotel property management system I've seen lets Front Desk representatives hide parts of folio or split them. This is allowed for two reasons. First, some guests need a "clean" folio that only shows room and tax. So, the Front Desk will either hide all other charges (food and beverage, for example) or split them into a separate folio.

The other reason why hiding/splitting is necessary is to fix mistakes. Being humans, Front Desk representatives sometimes do things like post a charge when they meant to post a credit. Then, they need to post a credit to fix the error plus another credit. That can get confusing pretty quickly because some charges also come with 1, 2, or even 3 lines of additional taxes.

The entire folio must balance or the Front Desk representative can't close out their shift. But, sometimes they might make a mistake and hide a charge that needs to be visible to make sense to the guest.

That's my guess on why the folio in question doesn't seem to be adding up correctly.

Example:
The following web page may give you an idea about the concept. The different folio views are examples of ways the system "hides" part of the folio. For example, Folio 9 view only shows charges that were reversed due to errors.

And the section entitled Folio Appearance lists ways to hide certain types of transactions.

How to View a Guest Folio | Front Office | Support Centre