So this was somehow caused by the ftbfs fix for klibc. On my eoan system:
mwhudson@anduril:~/images$ sudo /usr/lib/klibc/bin/losetup -f
loop: can't get info on device /dev/loop30: No such device or address
mwhudson@anduril:~/images$ sudo apt install klibc-utils=2.0.6-1ubuntu1 libklibc=2.0.6-1ubuntu1
[...]
mwhudson@anduril:~/images$ sudo /usr/lib/klibc/bin/losetup -f
/dev/loop30
So this was somehow caused by the ftbfs fix for klibc. On my eoan system:
mwhudson@ anduril: ~/images$ sudo /usr/lib/ klibc/bin/ losetup -f anduril: ~/images$ sudo apt install klibc-utils= 2.0.6-1ubuntu1 libklibc= 2.0.6-1ubuntu1 anduril: ~/images$ sudo /usr/lib/ klibc/bin/ losetup -f
loop: can't get info on device /dev/loop30: No such device or address
mwhudson@
[...]
mwhudson@
/dev/loop30