Why are my groups missing after restoring an ID backup?
For privacy reasons, groups are not managed on our servers but directly on users’ devices. Therefore, an ID backup will not suffice to restore groups.
After restoring an ID backup, groups you have not created yourself will appear once other group members have been active. Groups which you have created yourself, on the other hand, can only be restored using a data backup or an “Android Backup”.
As data backups cannot be used when switching operating systems (e.g., when moving from Android to iOS), you will have to recreate on your new device the groups you initially created on your old device.