I can recreate the issue following the steps in the initial description. Interestingly there are some (rare) cases where things works on 4.8 as well. There is a difference in udev messages:
Not working: KERNEL[3512.687794] change /devices/virtual/block/loop0 (block) KERNEL[3512.704230] change /devices/virtual/block/loop0 (block) KERNEL[3512.705301] change /devices/virtual/block/loop0 (block) UDEV [3512.732209] change /devices/virtual/block/loop0 (block) UDEV [3512.748186] change /devices/virtual/block/loop0 (block) KERNEL[3512.752751] change /devices/virtual/block/nbd0 (block) UDEV [3512.764683] change /devices/virtual/block/nbd0 (block) UDEV [3512.772212] change /devices/virtual/block/loop0 (block) KERNEL[3522.912384] change /devices/virtual/block/nbd0 (block) UDEV [3522.919200] change /devices/virtual/block/nbd0 (block)
Working: KERNEL[3528.095845] change /devices/virtual/block/loop0 (block) KERNEL[3528.124184] change /devices/virtual/block/loop0 (block) UDEV [3528.124410] change /devices/virtual/block/loop0 (block) UDEV [3528.144352] change /devices/virtual/block/loop0 (block) KERNEL[3528.148718] change /devices/virtual/block/nbd0 (block) KERNEL[3528.151216] change /devices/virtual/block/nbd0 (block) KERNEL[3528.151302] add /devices/virtual/block/nbd0/nbd0p1 (block) UDEV [3528.163222] change /devices/virtual/block/nbd0 (block) UDEV [3528.167442] change /devices/virtual/block/nbd0 (block) UDEV [3528.173677] add /devices/virtual/block/nbd0/nbd0p1 (block) KERNEL[3528.267889] change /devices/virtual/block/nbd0 (block) KERNEL[3528.269940] remove /devices/virtual/block/nbd0/nbd0p1 (block) UDEV [3528.275148] change /devices/virtual/block/nbd0 (block) UDEV [3528.276144] remove /devices/virtual/block/nbd0/nbd0p1 (block)
I can recreate the issue following the steps in the initial description. Interestingly there are some (rare) cases where things works on 4.8 as well. There is a difference in udev messages:
Not working: virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0 (block) virtual/ block/loop0 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0 (block)
KERNEL[3512.687794] change /devices/
KERNEL[3512.704230] change /devices/
KERNEL[3512.705301] change /devices/
UDEV [3512.732209] change /devices/
UDEV [3512.748186] change /devices/
KERNEL[3512.752751] change /devices/
UDEV [3512.764683] change /devices/
UDEV [3512.772212] change /devices/
KERNEL[3522.912384] change /devices/
UDEV [3522.919200] change /devices/
Working: virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/loop0 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0/ nbd0p1 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0/ nbd0p1 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0/ nbd0p1 (block) virtual/ block/nbd0 (block) virtual/ block/nbd0/ nbd0p1 (block)
KERNEL[3528.095845] change /devices/
KERNEL[3528.124184] change /devices/
UDEV [3528.124410] change /devices/
UDEV [3528.144352] change /devices/
KERNEL[3528.148718] change /devices/
KERNEL[3528.151216] change /devices/
KERNEL[3528.151302] add /devices/
UDEV [3528.163222] change /devices/
UDEV [3528.167442] change /devices/
UDEV [3528.173677] add /devices/
KERNEL[3528.267889] change /devices/
KERNEL[3528.269940] remove /devices/
UDEV [3528.275148] change /devices/
UDEV [3528.276144] remove /devices/