Issue with TLS and X509 authentication

Hi i have some issue connecting to my server that is secured with SSL. I have this working in Unity 2018.1 and set to .Net 4.x but when i updated to 2018.2.0 or 2018.2.1 it does not work anymore.

Error message: System.AggregateException: One or more errors occurred. ---> System.Security.Authentication.AuthenticationException: A call to SSPI failed, see inner exception. ---> Mono.Security.Interface.TlsException: Handshake failed - error code: UNITYTLS_INTERNAL_ERROR, verify result: UNITYTLS_X509VERIFY_FATAL_ERROR...

 public bool MyRemoteCertificateValidationCallback(System.Object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) {
         bool isOk = true;
         // If there are errors in the certificate chain, look at each error to determine the cause.
         if (sslPolicyErrors != SslPolicyErrors.None) {
             for (int i = 0; i < chain.ChainStatus.Length; i++) {
                 if (chain.ChainStatus[i].Status != X509ChainStatusFlags.RevocationStatusUnknown) {
                     chain.ChainPolicy.RevocationFlag = X509RevocationFlag.EntireChain;
                     chain.ChainPolicy.RevocationMode = X509RevocationMode.Online;
                     chain.ChainPolicy.UrlRetrievalTimeout = new TimeSpan(0, 1, 0);
                     chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllFlags;
                     bool chainIsValid = chain.Build((X509Certificate2)certificate);
                     if (!chainIsValid) {
                         isOk = false;
                     }
                 }
             }
         }
         return isOk;
     }
     public static FtpWebRequest GetFtpRequest(string directory) {
 
         ServicePointManager.ServerCertificateValidationCallback = AssetBundleManager.Instance.MyRemoteCertificateValidationCallback;
 
         FtpWebRequest ftpRequest = (FtpWebRequest)WebRequest.Create("ftps://" + AssetBundleManager.Instance.ipAdress + "/" + directory);
         ftpRequest.EnableSsl = true;
         ftpRequest.Credentials = new NetworkCredential(AssetBundleManager.Instance.username, AssetBundleManager.Instance.password);
 
         return ftpRequest;
     }
 
 

The error message is thrown when i try to get a response using:

FtpWebResponse response = (FtpWebResponse)ftpDirectoryRequest.GetResponse();

I had a similar issue in 2017.2 before i set the api compability level to .NET 4.x but then managed to get it working. Does anyone else have issues with this or does anyone see something wrong in my code?