The patches available in the Library vary depending on the Track Stack type, and which track in the Track Stack is selected:
When the main track of a folder stack is selected, no patches are available in the Library, and patches can’t be saved.
When the main track of a summing stack is selected, summing stack patches of a similar type are available in the Library.
For both types of stacks, when a subtrack is selected, patches for the appropriate track type are available.
If you choose a Track Stack patch when a subtrack of a folder stack is selected, the channel strip setting of the first subtrack of the same type in the Track Stack is loaded.