Can't Upgrade from 19.5.3 to 19.5.4

Howdy,

Before I engage in the time consuming and soul sucking experience of contacting Support, does anyone know why I'm getting the following when trying to upgrade 19.5.3 to 19.5.4 either though Download/Install via the Firmware page, or uploading the 19.5.4 image (downloaded and verified that checksums match what Sophos has published) to the other firmware slot?

Either process results in the green "Firmware validated successfully" notification followed shorty after by the red "New firmware could not be uploaded. Please refer to online help for possible reasons" error. Online help only has generic information, none of which is applicable to the scenario I'm facing.

Digging into /var/tslog/fwmgmt.log gives me the following:

Wed Mar 20 08:58:22 2024Z binary called with below parameter:
showfw -n 2
Wed Mar 20 08:58:22 2024Z [FWP0] read device bootdev name:'/dev/sda'
Wed Mar 20 08:58:22 2024Z [FWP0] reading bootimginfo from disk
Wed Mar 20 08:58:22 2024Z binary called with below parameter:
loadfw -v -f /sdisk/fwimg -D -P /tmp/prexfile -o 19_0_3_517
Wed Mar 20 08:58:22 2024Z [FWP0] read disk information '/dev/sda'
Wed Mar 20 08:58:22 2024Z [FWP0] read device bootdev name:'/dev/sda'
Wed Mar 20 08:58:22 2024Z [FWP0] reading bootimginfo from disk
Wed Mar 20 08:58:22 2024Z [FWP0] Extract/read firmware file '/sdisk/fwimg'
Wed Mar 20 08:58:31 2024Z [FWP1] New firmware name: 19_5_4_718
Wed Mar 20 08:58:31 2024Z checking bootimginfo '19_5_3_652'
Wed Mar 20 08:58:31 2024Z [FWP1] open prexfile '/tmp/prexfile' '32908800'
Wed Mar 20 08:58:33 2024Z [FWP1] running prex
Wed Mar 20 08:58:35 2024Z binary called with below parameter:
showfw -n 2
Wed Mar 20 08:58:35 2024Z [FWP0] read device bootdev name:'/dev/sda'
Wed Mar 20 08:58:35 2024Z [FWP0] reading bootimginfo from disk
Wed Mar 20 08:58:36 2024Z binary called with below parameter:
loadfw -l -f 1
Wed Mar 20 08:58:36 2024Z updateflags: zd=/dev/sda
Wed Mar 20 08:58:36 2024Z [FWP0] read device bootdev name:'/dev/sda'
Wed Mar 20 08:58:36 2024Z [FWP0] reading bootimginfo from disk
Wed Mar 20 08:58:36 2024Z FW0 : SFLoader [Boot value: 0]
Wed Mar 20 08:58:36 2024Z FW1 : 19_5_3_652 [Boot value: 1]
Wed Mar 20 08:58:36 2024Z FW2 : 19_0_3_517 [Boot value: 1]
Wed Mar 20 08:58:36 2024Z Default Firmware : 1
Wed Mar 20 08:58:36 2024Z Current Firmware : 1
Wed Mar 20 08:58:36 2024Z Last Firmware : 1
Wed Mar 20 08:58:36 2024Z [FWP6] Updateflag requested for firmware 1 : Boot code: -1, Set lastimage: 1, Set defaultimage: 0
Wed Mar 20 08:58:36 2024Z setting lstimg to 1
Wed Mar 20 08:58:36 2024Z binary called with below parameter:
loadfw -v -f /sdisk/fwimg -o 19_0_3_517
Wed Mar 20 08:58:36 2024Z [FWP0] read disk information '/dev/sda'
Wed Mar 20 08:58:36 2024Z [FWP0] read device bootdev name:'/dev/sda'
Wed Mar 20 08:58:36 2024Z [FWP0] reading bootimginfo from disk
Wed Mar 20 08:58:36 2024Z [FWP0] Extract/read firmware file '/sdisk/fwimg'
Wed Mar 20 08:58:45 2024Z [FWP1] New firmware name: 19_5_4_718
Wed Mar 20 08:58:45 2024Z checking bootimginfo '19_5_3_652'
Wed Mar 20 08:58:45 2024Z [FWP1] Read firmware kernel '10382336' bytes from firmware image
Wed Mar 20 08:58:46 2024Z [FWP1] copy installer kernel of '3623424' size
Wed Mar 20 08:58:46 2024Z [FWP4] Updating firmware kernel '/boot/19_5_4_718'
Wed Mar 20 08:58:46 2024Z [FWP4] Firmware kernel updated, removing older kernel file
Wed Mar 20 08:58:46 2024Z [FWP4] removing older kernel file '/boot/19_0_3_517'
Wed Mar 20 08:58:46 2024Z New firmware name: 19_5_4_718
Wed Mar 20 08:58:46 2024Z [FWP5] update squash fs info
Wed Mar 20 08:58:46 2024Z Update Squash: SQ_SIZE: 450310144,Flag: 1,Written at: 1065353216
set_loop loop0,loop5,loop6 and loop7 /dev/sda 1065353728 629145600 failed: No such file or directory

Anyone got any tips? Unable to upgrade to SFOS 20.0 at this stage so this is not an option.