I managed to reproduce this in a xenial vm on my machine. The problem appears with udev 243 it seems (installing udev and libudev 242-7ubuntu3 makes it work again).
When kpartx works it prints this message:
root@c:~# kpartx -av image.img
/dev/mapper/loop0p1 not set up by udev: Falling back to direct node creation.
add map loop0p1 (252:0): 0 2088960 linear 7:0 4096
so for some reason it's not getting to that fallback. FWIW, that fallback code is in libdevmapper (src:lvm2).
I managed to reproduce this in a xenial vm on my machine. The problem appears with udev 243 it seems (installing udev and libudev 242-7ubuntu3 makes it work again).
When kpartx works it prints this message:
root@c:~# kpartx -av image.img
/dev/mapper/loop0p1 not set up by udev: Falling back to direct node creation.
add map loop0p1 (252:0): 0 2088960 linear 7:0 4096
so for some reason it's not getting to that fallback. FWIW, that fallback code is in libdevmapper (src:lvm2).