Upgrading LrC to version 11 issues

I must be misunderstanding you because what you describe seems like normal behavior.

When you create the child collection set, it is not officially a child of the first collection set until AFTER you go through viewForCollectionSetSettings and SAVE it. The first time you enter viewForCollectionSetSettings, the drop down box in the UI may be showing the first collection set but that is a field in the property table, not the info.parents field. info.parents will be nil when you first create the child collection set even though the first collection set is selected in the drop down.

The 'child' collection set is not actually a child collection set until it is saved with a parent selected.

My senirio is:
I'm create a collectionSet via: 'publishService:createPublishedCollectionSet', than after that I wan't to create another collectionSet that is the child of the previous created collectionSet and 'info.parents' in equal to nil in  'viewForCollectionSetSettings'. 

Despite reverting to older versions, the issue still occurs, so I suspect it may be a local problem.
After deleting LrC and reinstalling it again, the 'parents' attribute is still nil.
Is there a way I can delete LrC completely (without any cache)? 

Any Ideas? 

Thanks for helping

I did explicitly check it again before I posted my last reply and the behavior I described was verified in my debug log. The only time I get 'nil' for info.parents is on creation of a new collection/collection set before it is saved. Once the collection/collection set has been saved, there is always an info.parents field and it has either an empty array for a top level collection or the appropriate array of parents for a non-top level collection.

To be clear, when you say 'the parents attribute is just not there', that is exactly the same as when I say info.parents is 'nil'. In LUA, a missing field is 'nil'. LrC does not initilize this field as an empty array on the first call to 'viewForCollectionSettings' when the collection is being created.

Are you saying that after you've created a new collection/collection set AND saved it, then edit that collection you are getting a nil info.parents field?

I'm aware of the desirable behaviour.
I stopped getting the 'parents' attribute after upgrading the LrC V11.2. 
I'm Logging the info element on either 'viewForCollectionSetSettings' or 'viewForCollectionSettings' and the parents attribute is just not there. 
I tried to uninstall and install Lightroom and it didn't help,

Can you check? 

You didn't say which version you upgraded to but with LrC v11.2, it works as expected. On the first call to 'viewForCollectionSetSettings' or 'viewForCollectionSettings' when the published collection or published collection set is being created, the info.parents is 'nil' because it hasn't been set, yet. The parent collection set can be changed by the user via the drop down box in the dialog. If you want to know which prospective parent is currently selected (and would be set upon save), you would have to bind/observe that property table field.

After the published collection/collection set has been created, subsequent calls to edit the collection have a valid info.parents field.

Are you seeing behavior different than this?