Live USB: "mount: /run/miso/sfs/rootfs: can't read superblock on /dev/loop3"

I messed up my existing Manjaro installation on a somewhat old computer, so I wanted to use a live USB boot. Since that one was also quite old, I wanted to install a new one there first. With both KDE and Gnome, I tried this command:

dd if=….iso of=/dev/sdc bs=1M status=progress

No errors there, checksum was correct, resulting partition looks big enough in GParted, but when I actually want to use it, I get this (may contain typos, can’t copy+paste):

Starting systemd-udevd version 252.5-1-manjaro
mount: /run/miso/sfs/rootfs: can´t read superblock on /dev/loop3
       dmesg(1) may have more information after failed mount system call.
ERROR; Failed to mount 'dev/loop3'
   Falling back to interactive prompt
   You can try to fix the problem manually, log out when you are finished
sh: can´t access tty; job control turned off
[rootfs ]# 

The output of “dmesg” is way too long to type it all, should I attach photos? The bits that seem relevant to me are:

loop0: detected capacity change from 0 to 292688 (4 times with different numbers) and then…
kworker/u8:3: attempt to access beyond end of device …and…
sdb: rw=524288, sector=7963540, nr_sectors = 8 limit=7866368
…a couple of times with different numbers, some of them followed by:
I/O error, dev loop3, sector 2054016 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2 (also with different numbers) and at the end…
SQUASHFS error: Failed to read block 0x3eb055af: -5
unable to read xattr id index table

Is this an issue with all current downloads, am I doing something wrong or is the USB drive itself maybe broken (seems fine when writing, though)? Is there any other information I can get out of this while in simplified command mode?

Did you use sync after the write, but before you unplug or reboot? :thinking:
(It might not have written all data to it yet…)

Notifications were off for some reason, I thought nobody had replied!
No, I didn’t do that. I would assume that the “safely remove” thing from the KDE tray should do that, but I’ll try it anyway now.

Tried it, still the same. “Safe remove” was much faster after “sync”, so I guess it’s included in that.