Xcode 12.0 Beta Missing autocompletion for classes which adopts a protocol

Usually I write a subclass of NSObject which implements UITableViewControllerDataSource and start to write number which leads to an autocomplete with suggestions from mentioned protocol but in Xcode12 the autocomplete returns empty list.

STR:

• move a cursor to body of class CountriesTableDataSource

• start to write "numb" which should lead to an autocomplete list of methods from UITableViewDataSource

Code Block 
class CountriesTableDataSource: NSObject, UITableViewDataSource {
    let data = Locale.isoRegionCodes.map {			Locale.current.localizedString(forRegionCode: $0) }
}