Problem with activation solved. I have been using virtualised Windows 7 for Mervis programming (and activation) without any trouble until Mervis 2.4 and it seems there is some problem with SSL with current Mervis version and this outdated OS. Everything else works fine, only the activation process fails. With Windows 10 I was able to finish activation as usual.
But there is still problem with MervisDB and Proxy communication. SslHanshakeError persists.