It appears to me that the following categories are duplicates:
https://www.wikitree.com/wiki/Category:Sydenham,_Kent
and
https://www.wikitree.com/wiki/Category:Sydenham,_Kent_(London).
Note that the CIBs both link to the same Wikipedia article and the same Vision of Britain page.
Edited to add:
I have just noticed another pair of duplicates too:
https://www.wikitree.com/wiki/Category:South_Norwood,_Surrey
https://www.wikitree.com/wiki/Category:South_Norwood,_Surrey_(London)
Thanks Roy.