After a few hours of poking around on these forums and my system, I think I fixed it. For anyone else in a similar situation, I followed the excellent guide found here on deleting the docker.img file and re-creating it. https://forums.unraid.net/topic/36647-official-guide-restoring-your-docker-applications-in-a-new-image-file/ Apparently when I did that earlier something must have not worked (or I didn't fully complete it) but following the steps below solved it and I re-added all my containers without issue. I can only guess that my recent container updates must have affected the size as it was over the 70% threshold. This time when re-creating it I doubled it to 40Gb which should give me more breathing room.