You may encounter an issue where a particular SmartObject gets duplicated (with the same version). Moreover, when navigating to the category where the SmartObject resides in K2 Management, you are seeing the error below:
An Item with the same key has already been added.
In K2 Designer, edit the SmartObject in question, then click on Finish without making any changes. This should remove the duplicate SmartObject automatically so that only one instance of the SmartObject exists.