It seems DateFormatter.date(from:) can't parse any date string in TimelineProvider.getTimeline(in:completion:) while DateFormatter.string(from:) works.
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "yyyyMMdd"
let date = formatter.date(from: "20201006")
let string = formatter.string(from: Date())
Result:
date = (Date?) nil
string = (String) "20201006"
Is it a bug or am I doing wrong?