Thanks to Soren Hansen for determining that /sys/module/nbd/parameters/max_part was set to 0. I'm not sure if the module was getting loaded before my script (which loads nbd with max_part=15) with the upstream default of '0' now and it wasn't before, but this fixes it for me:
$ sudo rmmod nbd
$ sudo modprobe nbd max_part=15
Thanks to Soren Hansen for determining that /sys/module/ nbd/parameters/ max_part was set to 0. I'm not sure if the module was getting loaded before my script (which loads nbd with max_part=15) with the upstream default of '0' now and it wasn't before, but this fixes it for me:
$ sudo rmmod nbd
$ sudo modprobe nbd max_part=15