I had a similar problem. I encrypt the backups. The container partition that holds the encrypted partition had a corruption. TM took forever to backup, and then

I had a similar problem. I encrypt the backups. The container partition that holds the encrypted partition had a corruption. TM took forever to backup, and then failed. Deleting the encrypted partition didn't solve the problem. Although this is not related to TM, it had the same effect. I didn't try to restore from this backup, looking back that was a mistake, just to see if that still worked. I had to erase the disk, create a new container partition and a new encrypted partition, and now it works. I use Crashplan as well, two external disks, one offsite, one of 4TB with three partitions, one for TM, two to sync a backup using Superduper - the paid version that just backs up the difference. I hope this is good enough.