Incomplete filevault encryption - endless restarts

Machine is a new Mac Mini, 1TB with fusion drive and High Sierra. I turned on FileVault completion, then selected 'update all' in the App Store, which included the latest macOS update from last week or so. The subsequent restart partially fails: at first it looks like a normal login - I see my username, my icon, and mountains in the background. I successfully enter my password. I see the progress bar (at first against the mountains like normal, then goes to a black-screen progress bar). Then a dialogue box pops up in the middle of the black macOS could not be installed on your computer The path /System/Installation/Packages/OSInstall.mpkg appears to be missing or damaged Quit the installer to restart your computer and try again.

Following the instructions and clicking the 'Restart' button leads to the same thing happening. I've tried this perhaps 5 times.

Next, I booted into recovery mode. My first step was to use the MacOS Reinstaller. I can get past the first couple of screens (agree to the statement). It asks me for the password to unlock the disk, which I do successfully. But for the next option

Select the disk where you want to install macOS

, my single disk (Macintosh HD) stays grayed out and un-selectable. I've waited for about 10 minutes at this screen, and there's been no change. If I double click the disk icon I get the message:

FileVault conversion in progress. Use the "Security and Privacy" preferences pane to check conversion status

With this in mind, another user suggested

fdesetup status

, but this command isn't found by the recovery mode terminal

Here's the output from

diskutil cs list

:

Logical Volume Group

-----

Name:Macintosh HD

Status: Online

.

.

.

Physical Volume ..

-----

disk:disk0s2

status: online

.

.

.

Physical Volume...

-----

disk: disk1s2

status: online

.

.

.

Logical Volume Family...

encryption type: AES-XTS

encryption status: unlocked

conversion status: converting (forward)

.

.

.

Logical Volume...

Disk: disk21

Status: Online

Conversion Progress: Paused

Revertible: No

As suggested by another user, I tried the following:

fsck_cs -y disk21

:

The volume disk 21 cannot be repaired when it is in use

Content Hint for disk21 is not Apple_CoreStorage

disk21: scan for volume headers invalid volume header @ 0: incorrect block type invalid volume header @.. : incorrect block type disk 21 is not a core storage volume

fsck_cs -y disk1s2

:

the volume disk1s2 cannot be repaired when it is in use Logical Volume Group ..

spans 2 devices Incomplete or inconsistent CoreStorage Physical Volume set

fsck_cs -y disk0s2

:

the volume disk0s2 cannot be repaired when it is in use logical volume group ..

spans 2 devices incomplete or inconsistent CoreStorage Physical Volume Set

Does it look like filevault is still working? One volume has status of paused, but another says converting. Is it a good idea to leave it turned on for several hours to complete encryption? I would be very grateful for any guidance.