Bad magic number in super-block while trying to open loop device

[JohanNicander]

Setup

OS: Ubuntu 20.04.5 LTS (bare metal)
sd-card OS: Raspberry Pi OS Light (64-bit)

Steps to reproduce error

Clone the sd card (same results using dd)

$ pv < /dev/sda > my-image.img

Run PiShrink

$ pishrink.sh my-image.img
pishrink.sh v0.1.2
pishrink.sh: Gathering data ...
tune2fs: Bad magic number in super-block while trying to open /dev/loop6
tune2fs 1.45.5 (07-Jan-2020)
pishrink.sh: ERROR occurred in line 298: tune2fs failed. Unable to shrink this type of image

Extra info

$ file my-image.img
my-image.img: DOS/MBR boot sector; partition 1 : ID=0xc, start-CHS (0x40,0,1), end-CHS (0x3ff,3,32), startsector 8192, 524288 sectors; partition 2 : ID=0x83, start-CHS (0x3ff,3,32), end-CHS (0x3ff,63,32), startsector 532480, 30384128 sectors

$ fdisk -l my-image.img
Disk my-image.img 14.74 GiB, 15829303296 bytes, 30916608 sectors
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: 0x8b97fb85

Device         Boot  Start  End      Sectors  Size  Id Type
my-image.img1        8192   532479   524288   256M  c  W95 FAT32 (LBA)
my-image.img2        532480 30916607 30384128 14.5G 83 Linux

mount -t ext4 my-image.img /mnt -o loop,offset=272629760,ro
mount: /mnt: wrong fs type, bad option, bad superblock on /dev/loop2, missing codepage or helper program, or other error.

[fredrikfalkman]

I have had the same problem running Pishrink on Mac, Ubuntu and Raspian. Also trying to compress Raspberry Pi OS Light (64-bit) 24Gb SD card.

[Drewsif]

So that error usually means the OS does not know what the partitions filesystem is. Can anyone confirm if the partition layout changed in the latest Raspberry Pi OS Light?

[develcore]

Same error.

OS: Debian Bullseye
sd-card OS: Raspbian Buster
mmcblk0p1 is fat32.
mmcblk0p2 is f2fs.