During the setup of an iOS device you have the option to restore from a previously created iCloud backup.
It is important to note this backup includes the supervision state of the device as it was.
When you restore from a backup onto the same iPhone, iPad, or iPod touch, your supervision state is restored from your backup. This will overwrite the new supervision state that was created when the device was re-enrolled into your MDM.
This will cause issues including VPP apps not being able to be installed. The app icon will now show a cloud icon by its name indicating it was unable to be installed.
To be able to restore from an iCloud backup and preserve the correct supervision identity, it's important you restore onto a different iPhone, iPad, or iPod touch, then your supervision state comes from Apple Business Manager or Apple School Manager and will be correct for that enrolment.