Procon doesn't connect - inactivity timeout

I am having issues connecting to procon. I am hosting the server on Ubuntu 18.04 with fun-bots mod. When I run the server with default ports, the RCON fails to start at all (getting error in the server launch messages). I set the RemoteAdminPort to 47201 and now the initial connection is done but Procon fails to connect stating that it times out (2 minutes of inactivity). Looking at tcpdump on server side, i can see Sync, Push and ACK packets flow but they jst stop at one point, and after 2 minutes it’s just Fin-FinAck.