How to restore apps on iPod?
If you updated iTunes to 12.7 then that explains the missing app loading.
Try to go back to iTunes 12.6 and then check. If the apps are still missing, you may need to restore them from a backup before iTunes 12.7 changed the syncing of apps to your device.
- https://www.macworld.com/article/3230135/software-entertainment/how-to-install-itunes-1263-and-replace-itunes-127.html