FileManager.default.contentsOfDirectory claims that the documents directory does not exist, even though it clearly does. I'm using Swift 4.2 on my actual iPhone SE running iOS 12.1.2

I am reading the contents of the downloads directory in my app using the following:

do {
    let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let downloadedContents = try FileManager.default.contentsOfDirectory(at: documentsURL, includingPropertiesForKeys: nil)
    print(downloadedContents)
} catch {
    print("Error while enumerating contents: \(error.localizedDescription)")
}

This prints the following, telling me that a file exists in the documents directory:

[file:///private/var/mobile/Containers/Data/Application/698F8D51-92AF-4BAB-A212-0A0982090550/Documents/example-file/]

(I moved the file there from the caches directory after downloading an in-app purchase, but I don't think that's relevant to this question).

Later in my code, I want to check if the file was downloaded. I'm using the following:

let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
let path = URL(fileURLWithPath: "example-file", relativeTo: documentsURL)
var isDir : ObjCBool = false
if FileManager.default.fileExists(atPath: path.standardizedFileURL.absoluteString, isDirectory: &isDir) {
    if isDir.boolValue {
        return true
    } else {
        return false // file exists but is not directory
    }
} else {
    return false // file does not exist at all
}

But this always returns false, even though contentsOfDirectory showed it exists.

While debugging, I also tried:

let fileManager = FileManager.default
let documentsURL = fileManager.urls(for: .documentDirectory, in: .userDomainMask)[0]
po FileManager.default.fileExists(atPath: documentsURL.standardizedFileURL.absoluteString)

But this, too, returns false. Now I'm pretty sure I'm just using the fileExists methods incorrectly.

Can anyone spot what I'm doing wrong?