Question: "Time Machine Backup Failed" since upgrading to Mojave
I am using Time Machine (TM) to back up to a 2 TB partition on a 4 TB external LaCie Porsche HD.
On Monday (9/24/2018) I upgraded to Mojave (Mac OS 10.14). On Tuesday, I got a message that my external HD didn't have enough space and TM wanted to erase an old backup from 3 years ago to make space. I gave it permission to do so, and all proceeded as normal.
It appears when looking in the Backups folder that there were 7 more backups that went well UNTIL the 26th and I started getting "Time Machine Backup Failed" messages. I've run Disk First Aid on the disk twice. By way of the Finder, I have removed 7 or 8 backups from 3 years ago. (Strangely, it says that I have freed up 600 GB. Which doesn't seem right since there are scores more backups still on the drive than the 8 that I deleted!) I restarted my Mac each time after I deleted and emptied the trash with the old backups.
Now the old drive was formatted as Mac OS X Extended (Journaled). Is that in conflict with the new APFS that Mojave uses? Do I have to reformat the partition of my external HD so that the backups will work normally? Will have to erase ALL of the partitions of my external HD!? (I don't want to do that since I have other important stuff on the other partitions.)
If anyone has any answers, please let me know ASAP.
iMac, macOS Mojave (10.14), 16 GB RAM, 1 TB HD