iOS OneDrive does not show all files and folders visibile in web application

I have some folders in our sharepoint site that are visible in the web application (e.g. web browser at https://ourcompany.sharepoint.com/sites/OurSite

But they are not visible in the iOS OneDrive application.

I'm logged in using my work credentials.

Most of the folders/files visible on the web application are visible in the iOS application but some are not.