Lets suppose you are connected – via the VPN – with screen in a remote server when you lost your connection, the VPN is down and your screen session still attached in the remote server. How to get back the unattached screen? First, redo your login, reopen your ssh and get back access to your remote server.
After restore your connection, you should use screen to list session still attached:
[root@localhost ~]# screen -ls There is a screen on: 16176.pts-0.localhost (Attached) 1 Socket in /var/run/screen/S-root.
Now is simple, just call screen with -U -R to get back your session:
[root@localhost ~]# screen -U -R
And you will be back on track 
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