Cannot reattach to a screen session after SSH connection was dropped
Solution 1:
I think you should try
screen -DR
next time too - the angry (uppercase) invocation should force it to disconnect that other session being held by your intermediate netcat hop.
Solution 2:
As suggested by Jens Timmerman, the ultimate reason for this strange behavior was that I was connecting to the remote server using SSH ProxyCommand and ncat. After killing the ncat on the intermediate machine, I am able to reattach to the screen session.