fusion drive issues on 2017 iMac

hello all,

I have had a 2017 iMac running macOS Catalina for several months without issue.

My workflow includes several OWC dual bay external hd enclosure containing SSD drives.

One of the OWC enclosures I purchased used on eBay and it had been acting up lately. Power

going off and the drives would be ejected without being unmounted from the desktop.

One of the drives in the eBay enclosure I use as a scratch disk for Photoshop. On several recent occasions the scratch disk ejected unexpectedly while I was working on photoshop files.

This caused an error message in Photoshop and I had to force quite the app.

Not long after this when I booted up the iMac, none of the applications would open.

I did a disk utility First Aid on the three volumes in the Fusion Drive. The HDD and the SSD

were fine. First Aid indicated that there was corruption on that volume that needed repaired (possibly due to the photoshop incidents listed above??).

I booted in Recovery mode and ran disk utility on all three volumes. Again, HDD and SSD volumes checked out. The APFS volume however gave the following upon checking the ‘object map’:

error: btn: invalid key order (45) old 1214959 / oxid 0 / level 0 /flags 0x6

previous key: 76 59 02 80 00 00 00 00 29 eb 3c 00 00 00 00 00

current key: 79 59 02 00 00 00 00 00 29 eb 3c 00 00 00 00 00

next key: 7c 59 02 00 00 00 00 00 29 eb 3c 00 00 00 00 00

Object map is invalid.

The volume /dev/rdisk3s1 could not be verified completely

File system check exit code is 8.

Restoring the original state found as mounted

File system verify or repair failed. : (-69845)

Operation failed…

After trying various solutions, I accidentally erased the APFS volume. Now, the computer

won’t even recognize an external startup volume. I can surf to the internal fusion drive when

booting in Recover. The only way that I can see to reverse my mistake with the APFS volume is to choose ‘Restore’ in Disk Utility. It asks to choose a volume to restore from and there are no choices. I do not use Time Machine.

I tried doing a clean install of Catalina but I get a message saying ‘cannot install, the container is incomplete’.

Can anyone suggest a solution for this dilemma short of taking the machine to an authorized Mac repair shop?

Thanks.

Dennis