This volume is not a supported Core Storage configuration.

I'm having trouble updating the OS on my Late 2013 iMac. I think the problem stems from the fact that about two years ago, I had the fusion drive replaced with an SSD, but I'm not sure how to fix it.

Here's what I know -

I was able to update my operating system to High Sierra (original release) with no trouble, BUT I haven't ever been able to install an update - every time it attempts, it restarts and then tells me some updates were unable to be installed. I tried several troubleshooting steps, including trying to install in recovery mode. It's been a while since I attempted an update, so I can't remember exactly what I tried, but I'm happy to give anything a go. Based on what I found there, I remember thinking that the system thought the fusion drive was still installed, and that was creating the issue. (?)

Today, I tried to install Mojave, thinking it might bypass the issue. When attempting to install, it says 'This volume is not a supported Core Storage configuration.' It doesn't appear that my disk is currently converted to APFS, but when I attempt to do that in Disk Utility, the option is greyed out.

Here's the output from diskutil in Terminal -

Device Identifier: disk2

Device Node: /dev/disk2

Whole: Yes

Part of Whole: disk2

Device / Media Name: SPCC Solid State Disk

Volume Name: Macintosh HD

Mounted: Yes

Mount Point: /

Content (IOContent): Apple_HFS

File System Personality:
Journaled HFS+

Type (Bundle): hfs

Name (User Visible): Mac OS Extended (Journaled)

Journal: Journal size 90112 KB at offset 0x1f73000

Owners: Enabled

OS Can Be Installed: Yes

Booter Disk: disk0s3

Media Type: Generic

Protocol: SATA

SMART Status: Not Supported

Volume UUID: 83E9DBB3-64A9-3F2C-AFB6-ECEC9ECE87DE

Disk / Partition UUID: 2CA9E6A9-27EA-47CB-802F-4988CDB7452A

Disk Size: 1.1 TB (1079982030848 Bytes) (exactly 2109339904 512-Byte-Units)

Device Block Size: 512 Bytes

Volume Total Space: 1.1 TB (1079982030848 Bytes) (exactly 2109339904 512-Byte-Units)

Volume Used Space: 547.0 GB (547020333056 Bytes) (exactly 1068399088 512-Byte-Units) (50.7%)

Volume Available Space:
533.0 GB (532961697792 Bytes) (exactly 1040940816 512-Byte-Units) (49.3%)

Allocation Block Size: 4096 Bytes

Read-Only Media: No

Read-Only Volume: No

Device Location: Internal

Removable Media: Fixed

Solid State: Yes

Virtual: Yes

OS 9 Drivers: No

Low Level Format: Not supported

Device Location: "SSD"

This disk is a Core Storage Logical Volume (LV).
Core Storage Information:

LV UUID: 2CA9E6A9-27EA-47CB-802F-4988CDB7452A

LVF UUID: 5657EE59-2576-465B-9D03-93661F30802E

LVG UUID: 8C09CF2F-356A-4379-AD35-B5B25B2EA28D

PV UUID (disk): 9FCDD4D8-88E2-4169-B252-54B020B835EB (disk1s2)

PV UUID (disk): 8C6342BA-6381-45A1-8B17-7763B4B07D14 (disk0s2)

Fusion Drive: No

Encrypted: No

Any ideas? Would be so grateful for any help. This is driving me nuts!