I've got the same issue. My mistake was in the syntax of the code. e.g.：guard let cell = cell as? FWTableViewCell else return { cell }. The key point of the mistake is 'guard let cell = cell '. Fix: guard let tempCell = cell as? FWTableViewCell else return { cell }

I get the same question, and I have tried restarting Xcode or restarting your Mac, but it's an error.