Restored the databases and did the upgrade again. Now I've all classes in all sites. So it seems that something did went wrong the first time, but I overlooked it.
I'm sorry that I was a little to fast to post this issue.... because it's not an issue.....
I had the same problem. I had to look in the database the id of my classes and I had to go on the /content/edit/idclasse URL to translate the name of the classes.
