Time Machine won't backup after upgrade to 10.14.4

That's good news, Jon, Ergg, and eagle! This is one of those times when an update corrects the errors of a previous update. 😺

Indeed. What a relief.

it took them six weeks lol.

Such patient waiting for a blessed event. Who says there's no mystery in computers?

This is the same thing that happened for me. Hard restart, backup worked once, now back to it being blocked by filevault which isn't even turned on. I have to call them when I have time to sit and talk in front of the computer, chat support couldn't help.

Same problem since on the 4th of April installing the latest Mojave upgrade. Tried everything mentioned above and on some other threads, including the "Reset of NVRAM or PRAM" — and nothing has worked. After that reset and after previously turning off the Mac and unplugging it several times, I got one finished backup each time then the same problem and message (Time Machine did not back up because FileVault was encrypting or decrypting a disk. Backups will resume once FileVault finishes). Never turned on FireVault, and checked in the Activity Monitor that is was off.

I have three external backup drives with my desktop. Two are connected to the USB3 ports, one to a hub. I've run the Disc Utility First Aid on all, and on the computer's internal HD, and all checked out.

Maybe replacing the interior battery is the last step?

+1 on this issue. Never used FileVault on this machine, and been running successful backups for years until the latest OS update. TM backup works once after restart/PRAM reset but not subsequently. OS issue?

Same problem here. I have even installed 10.14.4 new via recovery ... didn't change anything. Time Machine will only run one time, than the error "FileVault bla bla bla" occurred. FileVault is not running, and never was. Even checked via fdesetup. A restart will "fix" the problem, but only for one backup. Than the same error occurs again until the next restart... very annoying.

Mine is also a late 2012 iMac (32GB ram), and I use a LaCie d2 3TB external disk drive for time machine (TM).

The engineers initially implied it may be the older hardware, so with the assistance of Apple telephone support as a last resort we had :

. used disk utility to verify and repair the hard disk, erase the hard disk

. install the virgin OS that was shipped with the machine, and then I updated to 10.8.5, 10.10.5, 10.11.6, 10.13.6, 10.14.4 in sequence

. restored user files from TM backup

and the File Vault error still had not gone away (though I never enabled file vault).

the diagnostic logs from the iMac are being shared with the engineers. It would help if more users log this issue with Apple if not already done so.

Cold/warm restart, then run the TM backup - is a workaround for me just now.

Boot into Safe Mode and try running a backup from there. If successful, reboot normally and run another backup.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing.

Yes, the second backup succeeded, despite spending over an hour in "Preparing Backup". Subsequent backups start immediately. It appears the first and second backups take a long time as Time Machine figures out the file structure and builds a snapshot - then it goes smooth.

I wish I could get back the 2 days I lost solving this.