Via the LND slack:
What's the best way to 'revive' an offline channel? So many of my channels are offline, and when I manually connect to the nodes it sometimes revives the channel, but sometimes I just get the "already connected to peer" notice. Anything else I can do? In one case a channel has been offline for a long time but I was able to create a new channel to the same peer.
Answer: Add unsafe-disconnect=1 to the conf file and disconnect/reconnect