For a month a backup would not work despite my reaching out to Acronis support. It seems that they don't escalate. They just hope the problem will go away. Finally I uninstalled Acronis and started a new backup which which has not failed BUT with 2.4 TB to back time remaining is supposedly 127 d 8h. The calculated time keeps getting longer. So far it seems to take about 10 days for 100 GB, so it will be about 240 days for 2.4 TB. That is about 8 months! Supposedly I have a subscription to unlimited space and I would has like to keep a backup of my external drive with time machine backups. I guess that would be another 8 months. Obviously unacceptable. My subscription is up in 3 weeks. I am still waiting to see if Acronis support will come up with a credible fix before then. In any case cancel automatic renewal. Maybe Acronis has decided to dump individuals for large enterprises. If so they will have succeeded with me.