QSSLSocket read fail on iOS

My app (iOS 9.x simulator) connects to my server (Win 64bit).

Both are written in Qt and they communicate over QSslSocket.
On Desktop it works perfect.

Running the app on the device simulator the QSslSocket (client side) emits error(QAbstractSocket::SocketError) with the following:

Socket state: 1
Socket state: 2
Socket state: 3
Socket state: 6
Socket state: 0
QAbstractSocket::SocketError(20)
"SSLRead failed: -50"

I found this error in Apple API error list:
https://www.osstatus.com/search/results?platform=all&framework=all&search=-50

it says, that:
Security
SecBase.h errSecParam
-50 One or more parameters passed to the function were not valid.

The strange thing is that is that everything seems to work with this error on server side.