If I'm understanding correctly, you noticed that while in landscape mode, your app folder isn't displayed properly. I will be happy to help.
Does this occur with all folders? I'd recommend removing the apps from the folder, restarting your device and create a new folder to see if it resolves this.
Just in case, here are the articles with steps to create the new folder and restart the device: How to move apps and create folders on your iPhone, iPad, or iPod touch
and Restart your iPhone, iPad, or iPod touch
Cheers.