Existing GPT partition table seems to get corrupted by installer

UPDATE:
I checked what clonezilla had to say about the partition setup and methinks I’ve found the culprit.
The partition table according to Clonezilla as specified by blkdev.list:

KNAME NAME SIZE TYPE FSTYPE MOUNTPOINT MODEL
*loop0 loop0 215.8M loop squashfs /usr/lib/live/mount/rootfs/filesystem.squashfs *
sda sda 238.5G disk TOSHIBA_THNSNF256GMCS
*sda1 |-sda1 2M part *
*sda2 |-sda2 6G part swap *
*sda3 |-sda3 23.5G part ext4 *
*sda4 `-sda4 196.9G part ext4 *
sdb sdb 3.8G disk iso9660

and blkid.list:

/dev/loop0: TYPE=“squashfs”
/dev/sda1: PTTYPE=“dos” PARTUUID=“7f7c8e18-6ec3-4121-a718-e1d538c9c9e2”
/dev/sda2: UUID=“58603e47-e21b-4519-9053-52ff3837f327” TYPE=“swap” PARTUUID=“5db51baf-eb15-43de-9bac-2e9acf521a57”
/dev/sda3: LABEL=“Elive_OS” UUID=“3501bf84-3c82-40d8-a58d-9d19d738b126” TYPE=“ext4” PARTUUID=“c2421657-d74d-41f7-a9e6-7c30df176044”
/dev/sda4: UUID=“9f3c5921-8053-4edd-9683-8a25381509c4” TYPE=“ext4” PARTUUID=“49bc50fb-4682-464d-a93f-f33d1e546dab”
/dev/sdb1: UUID=“2019-01-08-09-10-02-00” LABEL=“2.6.0-37-amd64” TYPE=“iso9660” PARTUUID=“495d5b6a-01”

Where the 12gb partition would be the rest of the 256 Gb disk i.e. unused in the scheme but was part of the prior Ubuntu install.

sda-gpt according to clonezilla:

Number Start (sector) End (sector) Size Code Name

  • 1 2048 6143 2.0 MiB 0700 *
  • 2 462249984 474898431 6.0 GiB 8200 *
  • 3 6144 49315839 23.5 GiB EF00 *
  • 4 49315840 462249983 196.9 GiB 8300*

This is the first time I’ve had these issues with clonezilla