ubuntu-studio installer hangs after "Disk setup" page

[fenugrec]

- boot ubuntu-studio 24.04 installer from USB drive
- make a weird partition setup (that should theoretically work)
- run ubuntu-desktop-boostrap
- follow steps; on the "Disk setup" page, select "Manual installation"
- click next
- Hang, with the following console output :

****************
flutter: DEBUG subiquity_client: GET http://localhost/storage/v2/orig_config
flutter: ERROR ubuntu_bootstrap: Unhandled exception
        SubiquityException: getOriginalStorageV2() returned error 500
Traceback (most recent call last):
  File "/snap/ubuntu-desktop-bootstrap/231/bin/subiquity/subiquity/common/api/server.py", line 164, in handler
    result = await implementation(**args)
  File "/snap/ubuntu-desktop-bootstrap/231/bin/subiquity/subiquity/server/controllers/filesystem.py", line 1059, in v2_orig_config_GET
    model = self.model.get_orig_model()
  File "/snap/ubuntu-desktop-bootstrap/231/bin/subiquity/subiquity/models/filesystem.py", line 1508, in get_orig_model
    orig_model.load_probe_data(self._probe_data)
  File "/snap/ubuntu-desktop-bootstrap/231/bin/subiquity/subiquity/models/filesystem.py", line 1994, in load_probe_data
    self.reset()
  File "/snap/ubuntu-desktop-bootstrap/231/bin/subiquity/subiquity/models/filesystem.py", line 1492, in reset
    self.process_probe_data()
  File "/snap/ubuntu-desktop-bootstrap/231/bin/subiquity/subiquity/models/filesystem.py", line 1512, in process_probe_data
    self._orig_config = storage_config.extract_storage_config(self._probe_data)[
  File "/snap/ubuntu-desktop-bootstrap/231/lib/python3.10/site-packages/curtin/storage_config.py", line 1372, in extract_storage_config
    found_cfgs, found_errs = parser.parse()
  File "/snap/ubuntu-desktop-bootstrap/231/lib/python3.10/site-packages/curtin/storage_config.py", line 641, in parse
    entry = self.asdict(data)
  File "/snap/ubuntu-desktop-bootstrap/231/lib/python3.10/site-packages/curtin/storage_config.py", line 800, in asdict
    raise RuntimeError(
RuntimeError: Couldn't find partition entry in table

#0 SubiquityClient._receive (package:subiquity_client/src/client.dart:74)
<asynchronous suspension>
#1 StorageService.getOriginalStorage.<anonymous closure> (package:ubuntu_bootstrap/services/storage_service.dart:126)
<asynchronous suspension>
#2 ManualStorageModel._updateOriginalConfigs (package:ubuntu_bootstrap/pages/storage/manual/manual_storage_model.dart:237)
<asynchronous suspension>
#3 ManualStorageModel.init (package:ubuntu_bootstrap/pages/storage/manual/manual_storage_model.dart:246)
<asynchronous suspension>
#4 DefaultEquality.isValidKey (package:collection/src/equality.dart:90)
<asynchronous suspension>
#5 WizardController._loadRoute (package:wizard_router/src/controller.dart:26)
<asynchronous suspension>
#6 WizardController.next (package:wizard_router/src/controller.dart:105)
<asynchronous suspension>
#7 NextWizardButton.build.<anonymous closure>.<anonymous closure> (package:ubuntu_wizard/src/wizard_button.dart:275)
<asynchronous suspension>
#8 _WizardButtonState.build.<anonymous closure> (package:ubuntu_wizard/src/wizard_button.dart:114)
<asynchronous suspension>

******************
current partition setup :

ubuntu-studio@ubuntu-studio:~$ sudo fdisk -l /dev/sda
Disk /dev/sda: 476.94 GiB, 512110190592 bytes, 1000215216 sectors
Disk model: SK hynix SC300 S
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: 0xf2489343

Device Boot Start End Sectors Size Id Type
/dev/sda1 2048 1126399 1124352 549M 7 HPFS/NTFS/exFAT
/dev/sda2 1126400 105983999 104857600 50G 83 Linux
/dev/sda3 105984000 917368831 811384832 386.9G 83 Linux
/dev/sda4 * 917368832 1000214527 82845696 39.5G 83 Linux

ubuntu-studio@ubuntu-studio:~$ sudo fdisk -l /dev/sdb
Disk /dev/sdb: 476.94 GiB, 512110190592 bytes, 1000215216 sectors
Disk model: SK hynix SC308 S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x0c8c7199

Device Boot Start End Sectors Size Id Type
/dev/sdb1 2048 278922916 278920869 133G 7 HPFS/NTFS/exFAT
/dev/sdb2 999092224 1000210431 1118208 546M 27 Hidden NTFS WinRE
/dev/sdb3 278923264 999092223 720168960 343.4G 5 Extended
/dev/sdb5 278925312 401805311 122880000 58.6G 83 Linux

Partition table entries are not in disk order.

*********************

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: subiquity (unknown)
ProcVersionSignature: Ubuntu 6.8.0-31.31.1-lowlatency 6.8.1
Uname: Linux 6.8.0-31-lowlatency x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.28.1-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.498
CloudArchitecture: x86_64
CloudID: nocloud
CloudName: unknown
CloudPlatform: nocloud
CloudSubPlatform: seed-dir (/var/lib/cloud/seed/nocloud)
CurrentDesktop: KDE
Date: Sat Jul 20 00:55:41 2024
DesktopInstallerRev: 231
LiveMediaBuild: Ubuntu-Studio 24.04 LTS "Noble Numbat" - Release amd64 (20240424.1)
SourcePackage: subiquity
Symptom: installer
UpgradeStatus: No upgrade log present (probably fresh install)