17.1 Wlp6s0: failed to remove key (1, ff:ff:ff:ff:ff:ff) from hardware (-22)

3 ways to fix this problem:

First way: If you don't wanna make change to grub or changing the grub create other problems or you don't wanna upgrade the kernel:

• Everytime when you see that error after turning off the pc,just press alt+F7.

Second way: Removing "quiet splash" from the parameters in grub:

• gksudo gedit /etc/default/grub

  Change:

  GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
  

  To:

  GRUB_CMDLINE_LINUX_DEFAULT=""
  

  Then run:

  sudo update-grub
  reboot
  

Third way:

• Upgrade to kernel 4.13.6 or higher.

I'm having this same issue, I'd be interested to see what the resolution is. I believe disconnecting from the Wireless connection will allow you to shut down gracefully if you haven't found out, but I'm not entirely sure how to resolve it either.

EDIT: Looks like this is resolved in a new kernel version, but I'd be interested to know if a fix exists.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1720930