I'm having the same issue. Here is my log:
YlandsLog {}
[IN] Ylands Version: 0.6.1.41937
[IN] command line arguments: C:\Program Files (x86)\Steam\steamapps\common\Ylands\Ylands.exe
[IN] Logging On
[EX]U InvalidProgramException: Missing or incorrect header for method InternalTransformFinalBlock
+t System.Convert.ToBase64String (System.Byte[] inArray, Int32 offset, Int32 length)
System.Convert.ToBase64String (System.Byte[] inArray)
Base.Json.JsonHelper.Write (System.Text.StringBuilder output, System.Byte[] value)
CoreServices.Model.Oauth.SteamTokenAuthReq.DoSerializeToJson (System.Text.StringBuilder output)
CoreServices.Model.Oauth.SteamTokenAuthReq.SerializeToJson (System.Text.StringBuilder output)
CoreServices.RestRequest.CreateUnityWebRequest (System.Text.StringBuilder builder, System.String baseUrl, System.String& optRequestBody)
CoreServices.CoreServicesManager+<SendRestRequestCoro>c__Iterator0`1[CoreServices.Model.Oauth.SteamTokenAuthResponse].MoveNext ()
UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
Base.Utils.CoroHostProvider:StartCoroutine(IEnumerator)
CoreServices.CoreServicesManager:SendRestRequest(String, String, RestRequest, Action`1, IRequestPostProcessor, Int32)
CoreServices.CoreAuthService:LoginWithPublisherTicket(IAuthTicket, Action`1)
ylands.Online.GameServicesManager:OnPublisherGetSessionTicketReceived(AsyncCallResult`1)
CoreServices.Publisher.Steam.SteamServicesProvider:OnGetAuthSessionTicketResponse(GetAuthSessionTicketResponse_t)
Steamworks.Callback`1:OnRunCallback(IntPtr, IntPtr)
Steamworks.NativeMethods:SteamAPI_RunCallbacks()
Steamworks.SteamAPI:RunCallbacks()
ylands.SteamIntegration.CommonSteamApi:RunCallbacks()
ylands.SteamIntegration.SteamManager:Update()
DxDiag.txt
output_log_clean.txt