AssetRegistrySearchable is listed as a Class Specifier on the Gameplay Classes page:
However, the specifier’s own page suggests it is a Property Specifier:
https://docs.unrealengine.com/latest/INT/Programming/UnrealArchitecture/Reference/Classes/Specifiers/AssetRegistrySearchable/index.html
(emphasis mine)
This is corroborated by the fact that the Properties page lists it as a Property Specifier:
I therefore think the AssetRegistrySearchable specifier needs to be removed from the Class Specifiers list, unless new functionality has been included to make it a Class Specifier as well (in which case the documentation page for AssetRegistrySearchable should be updated to reflect this).