SSL Handshake fail when trying to download a file from an FTPS

Question

What I'm doing?

I'm working on a iOS app which is going to download files from an FTPS server. For this purpose I'm using the library FilesProvider.

Error description

Until now I successfully achieve to login in the server, list files and search for files, but I'm getting the following error when trying to download one of the files:

File Provider <FilesProvider.FTPFileProvider: 0x283c23900> shouldDoOperation Copy with action Copying and destination file:///private/var/mobile/Containers/Data/Application/90AF4202-18C1-4A41-B461-4FB262FD39B9/tmp/B13A8110-C919-48E4-8BD9-E684929310C0.tmp
2020-05-27 14:35:39.372289+0200 MyApp[548:100799] [] nw_socket_handle_socket_event [C13:1] Socket SO_ERROR [54: Connection reset by peer]
2020-05-27 14:35:39.595959+0200 MyApp[548:99892] CFNetwork SSLHandshake failed (-9806)
2020-05-27 14:35:39.596380+0200 MyApp[548:99892] TCP Conn 0x28274f540 SSLHandshake failed (-9806)
File Provider <FilesProvider.FTPFileProvider: 0x283c23900> Failed for operation Copy with action Copying and destination file:///private/var/mobile/Containers/Data/Application/90AF4202-18C1-4A41-B461-4FB262FD39B9/tmp/B13A8110-C919-48E4-8BD9-E684929310C0.tmp
Throwing Error: Error Domain=NSOSStatusErrorDomain Code=-9806 "(null)" UserInfo={_kCFStreamErrorCodeKey=-9806, _kCFStreamErrorDomainKey=3}

FTPFileProvider is an object created with the library I've mention above that handles the FTP connection. That provider looks like:

guard let url = URL(string: "ftps://X.X.X.X") else { return } // I have to use an IP address instead of a domain
var provider = FTPFileProvider(baseURL: url, mode: .default, credential: credential, cache: .none)
provider.delegate = self
provider.fileOperationDelegate = self // This delegate is only for print the first line of the error
provider.serverTrustPolicy = .disableEvaluation

After creating the provider of the connection, I've been able to do login in the server, search some files and get the file list. I'm doing that with this function:

provider.searchFiles(path: remotePath, recursive: false, query: predicate, foundItemHandler: { (file) in print("File found with name: \(file.name)") }, completionHandler: { (list, error) in
        if error != nil {
            DispatchQueue.main.async {
                onError(error!)
            }
        } else {
            var files:[String] = []
            for f in list {
                (f.isRegularFile) ? files.append(f.name) : nil
            }
            DispatchQueue.main.async {
                onSucess(files)
            }
        }
})

When running that search I get this warning:

2020-05-27 14:45:51.831812+0200 MyApp[555:102153] [] nw_socket_handle_socket_event [C4:1] Socket SO_ERROR [54: Connection reset by peer]

But I successfully get an output in onSuccess(files). The returned value for files is:

["20200527-093234-28346646454.pdf", "20200527-105409-28346646454.pdf"]

After that search, I try to download one of the files is when I get the error describe at the beginning of this post. For do the download I have the following function:

provider.copyItem(path: "\(remotePath)/\(file)", to: localPath.absoluteString, overwrite: true) { (error) in
    if error != nil {
        DispatchQueue.main.async {
            onError(error!)
        }
    } else {
        DispatchQueue.main.async {
            onSuccess(localPath)
        }
    }
}

What I've try

• As you could see above, the object who connect to the server has disabled the SSL certificate checks. That's why I can do the login and search for the files.
• I've configure the Info.plist disabling ATS:

<key>NSAppTransportSecurity</key>
    <dict>
        <key>NSAllowsArbitraryLoads</key> <!-- Because I wan't to allow everything  -->
        <true/>
        <key>NSAllowsLocalNetworking</key> <!-- Because seems like library uses AVFoundation framework -->
        <true/>
        <key>NSAllowsArbitraryLoadsForMedia</key> <!-- Because I'm using a public IP instead a domain -->
      <true/>
    </dict>

Neither of that options works.

Some facts

• Domain DNS entry is not going to be created for now. I can't do anything about this.
• Server do have a valid SSL certificate.
• I can successfully login, list files and search for files. (I just can't download)
• I didn't try to upload a file. App isn't going to do it.

Questions

• Why login, listing or searching files works but I get that error when trying to download?
• Any idea on how to fix it? Any workaround?