Hi @StefanoSchiavini, I'd take a look in REST to see if the collaboration is there on the Enterprise side (check out the above post for the steps). There's also the option to remove the Enterprise guest and add again. This might be something good for Esri support to take a look at since you are experiencing the issue as well. They can also help troubleshoot your environment directly so we can understand the root cause and prevent it from happening in the future.
... View more