This method cannot add the first document to a folder that is “Shared, Personal on first use.”
And it also applies to PutAllInFolder. The folder must exist before documents can be added to it. The CreateOnFail does not work for this type of folder.
for the ones it’s working for, the private on first use folder probably already exists. otherwise, check the ACL and make sure the users in question have the ability to create private folders/views.