Shadowsocks is detectable using entropy analysis but not everybody does it. I heard in China they do. you connect at first they collect data, analyze and ban. in Russia they are not that smart yet but in Russia even if you mask VPN traffic they use other tricks. For example if you visit any state adjacent site from your Russian IP and VPN with same cookies they can ban VPN exit node. Or if all your traffic goes to one IP they will probe ports or just ban that.