Restoring might just work, but we want to avoid doing things all over again on the backup file. I have a few other solutions you can do to resolve this.
Note: The steps here are intended for updated versions of QuickBooks Desktop. We've discontinued support for the 2013 edition. You can still do these troubleshooting solutions however. That said, we recommend upgrading to the latest version to avoid or lessen issues when running the software.
As you've suspected, this might be related to QuickBooks itself. Though, we can first narrow it down to the company file. To fix this, you'll want to run the File Doctor. The full steps and details are found in this article: Fix company file and network issues with QuickBooks File Doctor.
After running the File Doctor, check the sort tool bar and the Filter By option. If you're still getting the same issue, then you'll want to clean uninstall and reinstall QuickBooks.
If you don't have the QuickBooks 2013 installer anymore, you can download it here. Simply select United Kingdom as your country, choose your version then QuickBooks 2013.
After fixing the issues, you might want to check out our articles if you need help managing your suppliers, bills and expenses. Go to the Expenses and suppliers topics to browse our help content. Looking for other topics instead? Scroll down to the bottom of the page for the More Help Topics section.
I'll help you out again if you have other concerns regarding QuickBooks Desktop. Just post your questions here in detail and I'll respond as soon as possible.