Fakeraid partition missing (not mapped as a device on boot) after upgrade to Ubuntu 22.04

I have a RAID-0 volume with an NTFS partition that has worked fine for years on my dual-boot system (readable and writable by both Windows and Linux). Today after doing a do-release-upgrade -d to upgrade to Ubuntu 22.04 (from Ubuntu 20.04), this filesystem isn't showing up in Ubuntu. The problem seems to be around device mapping; here's what I've tried/found so far: - It still works fine in Windows. I don't think anything changed on the disks. - An NTFS partition on a different disk (non-RAID) still mounts and works fine. - Booting into the old kernel (via grub) doesn't fix it (and seems to cause other problems). - I thought my setup was "hardware RAID" because I configured it via a BIOS boot screen titled "Intel Matrix Storage Manager", but I guess this is actually "fakeraid". - The RAID volume shows up in the Disks utility (as /dev/dm-0, and this file exists) with no partitions, just "unallocated space". - The RAID volume shows up in GParted (as /dev/mapper/isw_dfjaifidah_KarlsRaid, and this file exists) with an ntfs partition named /dev/mapper/isw_dfjaifidah_KarlsRaid1 (i.e. the volume name with a 1 appended), but that device file does not exist. The only file in /dev/mapper/ is isw_dfjaifidah_KarlsRaid. Here's the relevant part of sudo fdisk -l. (sda,sdb,sdc are the disks in the RAID array.)

Disk /dev/sda: 596.17 GiB, 640135028736 bytes, 1250263728 sectors
Disk model: WDC WD6401AALS-0
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x15967f5e

Device     Boot Start        End    Sectors  Size Id Type
/dev/sda1        2048 3750772735 3750770688  1.7T  7 HPFS/NTFS/exFAT


Disk /dev/sdb: 596.17 GiB, 640135028736 bytes, 1250263728 sectors
Disk model: WDC WD6401AALS-0
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x2a0921b8


Disk /dev/sdc: 596.17 GiB, 640135028736 bytes, 1250263728 sectors
Disk model: WDC WD6401AALS-0
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x2a0921bf


Disk /dev/mapper/isw_dfjaifidah_KarlsRaid: 1.75 TiB, 1920398131200 bytes, 3750777600 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 131072 bytes / 393216 bytes
Disklabel type: dos
Disk identifier: 0x15967f5e

Device                                     Boot Start        End    Sectors  Size Id Type
/dev/mapper/isw_dfjaifidah_KarlsRaid-part1       2048 3750772735 3750770688  1.7T  7 HPFS/NTFS/exFAT

The file /dev/mapper/isw_dfjaifidah_KarlsRaid-part1 (note the -part1) doesn't exist either. **I'm slightly worried by the fact that /dev/sda1 shows up**, since (if my assumptions are correct) we should only be looking for partition tables on the combined volume, not directly on a single disk in the array. **The file /dev/sda1 exists**, and sudo ntfs-3g.probe --readwrite /dev/sda1 reports "NTFS signature is missing". Maybe the system is finding my partition table on sda, even though that data is just part of a RAID stripe, and creating dev/sda1 based on it. I can imagine this causing some kind of name collision when the identical "real" partition table on the RAID volume is encountered. FWIW, hdparm -z /dev/mapper/isw_dfjaifidah_KarlsRaid outputs:

/dev/mapper/isw_dfjaifidah_KarlsRaid:
 re-reading partition table
 BLKRRPART failed: Invalid argument

That's pretty much where I'm stuck! How can I fix this? Thanks in advance for any suggestions - even obvious ones, since I don't really know what I'm doing. Some other notes (likely irrelevant): - Yesterday I upgraded from nvidia-driver-390 to nvidia-driver-470 via the gui "Additional Drivers" tool and had [this problem](https://ubuntuforums.org/showthread.php?t=2473057) where it switched me from a -generic to an -oracle kernel that didn't recognize my networking hardware. Wanting a newer (generic) kernel is what motivated me to do the distribution upgrade. - I wanted to do a clean install from the Ubuntu 22.04 Live CD (which I verified against the published checksum after burning), but it fails to boot ("Failed to start CUPS scheduler" after several minutes). - The do-release-upgrade went smoothly AFAICT except for an error about a handful of "mpi" packages at the end. Afterwards, apt commands were failing, with dpkg complaining that these packages were "not configured yet". I fixed this by reinstalling openmpi-bin as in [this answer](https://stackoverflow.com/a/62464086) . ---------- More output as requested in comments:

# lsblk -M -f
    NAME
     FSTYPE FSVER LABEL         UUID                                 FSAVAIL FSUSE% MOUNTPOINTS

[after a bunch of loop devices related to /snap/...]

┌┈▶ sda
     isw_ra 1.2.0                                                                   
├┈▶ sdb
     isw_ra 1.2.0                                                                   
└┬▶ sdc
     isw_ra 1.2.0                                                                   
 └┈┈isw_dfjaifidah_KarlsRaid
                                                                                    
    sdd
│                                                                                   
    ├─sdd1
│    ntfs         OCZ Vertex 4  1A7643E57643C06D                       58.6G    69% /mnt/WinC
    ├─sdd2
│    ntfs                       129E918C9E9168CD                                    
    ├─sdd3
│                                                                                   
    ├─sdd5
│    ext4   1.0                 5b327639-85e6-4f6a-ac79-743cfedf3e29   10.8G    64% /
    └─sdd6
     swap   1                   b601da00-767d-4e50-b62a-0b832992599c                [SWAP]

# partx /dev/mapper/ is isw_dfjaifidah_KarlsRaid
partx: bad usage
Try 'partx --help' for more information.

# partx /dev/mapper/isw_dfjaifidah_KarlsRaid   
NR START        END    SECTORS SIZE NAME UUID
 1  2048 3750772735 3750770688 1.7T      15967f5e-01

# partx /dev/sda                            
NR START        END    SECTORS SIZE NAME UUID
 1  2048 3750772735 3750770688 1.7T      15967f5e-01