Updating to Mojave & enabling FileVault at the same time Recently I decided to update to Mojave. Additionally, FileVault encyption was mandated remotely. Upon the reboot all hell broke loose.

The output of "diskutil apfs list" tells me Macintosh HD is "Not Mounted" while its Encryption Progress is stuck at 0.0% (Paused) (Locked).

Nothing seems to happen when I try to mount the drive using Disk Utility. Well, it does manage to unlock the drive after asking for the password (for some reason it doesn't accept the password the first time and I have to enter it twice). 

After a recovery reboot (at this stage the disk is locked):

# diskutil apfs unlockVolume disk2s1
Passphrase: (...)
Unlocking any cryptographic user on APFS Volume disk2s1
Error unlocking APFS Volume: Couldn't mount disk (-69842)


The disk is now unlocked.

# diskutil mount /dev/disk2s1
Volume on disk2s1 failed to mount; it appears to be an APFS Volume which might be locked
Try "diskutil apfs unlockVolume"

# diskutil apfs unlockVolume disk2s1
Passphrase: (entering the password here)
Unlocking any cryptographic user on APFS Volume disk2s1
Error unlocking APFS Volume: The given APFS Volume is not locked (-69589)

# diskutil mount /dev/disk2s1
Volume on disk2s1 failed to mount; it appears to be an APFS Volume which might be locked
Try "diskutil apfs unlockVolume"


# fsck_apfs /dev/disk2s1
** Checking volume.
** Checking the container superblock.
** Checking the EFI jumpstart record.
** Checking the space manager.
** Checking the object map.
** Checking APFS volume superblock.
** Checking the object map.
warning: omap (oid 0x9a64f): invalid om_flags (0x2)
mount_apfs: mount: Input/output error
error: mount_apfs exit status 73
** The volume /dev/disk2s1 could not be verified completely.


Now, after another fresh recovery boot I've done the following:


Unlocked the drive (unlockVolume) with the -nomount option.
Disk Utility > First Aid gave me the following


Repairing file system.
Volume is already unmounted. 
Performing fsck_apfs -y -x /dev/rdisk2s1
Checking volume.
Checking the container superblock.
Checking the space manager.
Checking the object map.
Checking the APFS volume superblock.
Checking the object map.
warning: omap (oid 0x9a64f): invalid om_flags (0x2)
error: er_state-&gt;esrb_version is 2, should be 1
Encryption Rolling data structures are invalid.
The volume /dev/rdisk2s1 could not be verified completely.
File system check exit code is 0.
Restoring the original state found as unmounted.
Operation successful.


The "error: er_state->esrb_version is 2, should be 1" and the "Encryption Rolling data structures are invalid" parts are new.

Thank you for your time.
Fixed! What helped to move the needle is Target Disk Mode. Another Mac was able to unlock and mount the disk and it eventually completed its encryption that was stuck at 0.0% otherwise.