Not OP but just upgraded on my own instance and one issue is that you have to give the lemmy_ui and pictrs containers access to the internet instead of just the local network by adding lemmyexternalproxy to the networks in docker-compose.yml. I did use the Lemmy-Easy-Deploy script made by /u/ubergeek77@lemmy.ubergeek77.chat but it should be the same when using ansible considering I adapted instructions for ansible from the Lemmy github issue tracker 😂 . If you don't do that you can't access the page and just see server_error on a blank page but works in an external client like jerboa.