AES256 metadata encryption in fw 1.9.0 means ... what exactly?

Does the new metadata encryption using AES256, introduced in firmware version 1.9.0 and later, mean that after an update, Nitrokey users should reset the NitroKeys if possible and recreate all the credentials stored on them?

Could someone explain in detail exactly what metadata this refers to (metadata within the flash file system or in other locations)?