prime-offload doesn't work

[graingert]

When I try to load the nvidia module it doesn't load.

$ sudo prime-select query
intel
$ sudo prime-offload
$ cat /var/log/prime-supported.log
Requires offloading
$ cat /var/log/prime-offload.log
Sorry the nvidia kernel module is not is loaded
$ sudo modprobe nvidia
modprobe: ERROR: ../libkmod/libkmod-module.c:832 kmod_module_insert_module() could not find module by name='off'
modprobe: ERROR: could not insert 'off': Unknown symbol in module, or unknown parameter (see dmesg)

Similar to https://bugs.launchpad.net/ubuntu/+source/bumblebee/+bug/1438106 but I'm not using bumblebee
Similar to https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-390/+bug/1774359 but I'm not sure if the bug is here or there

The file in this nvidia-graphics-drivers-390 package still has those aliases

$ cat /etc/modprobe.d/nvidia-graphics-drivers.conf
blacklist nouveau
blacklist lbm-nouveau
alias nouveau off
alias lbm-nouveau off

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: nvidia-prime 0.8.8
ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17
Uname: Linux 4.15.0-22-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.1
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu May 31 10:48:16 2018
Dependencies:

InstallationDate: Installed on 2018-05-30 (0 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: nvidia-prime
UpgradeStatus: No upgrade log present (probably fresh install)