Comment 36 for bug 1685794

To add to Andrew's solution, in my case, the UUID in /etc/initramfs-tools/config.d/resume was correct. But my swap was on an LVM partition.

I have found this blog post: https://www.hiroom2.com/2018/05/01/ubuntu-1804-lvm-swap-wait-for-root-en/

and changed the line in /etc/initramfs-tools/config.d/resume from using UUID to using device path of LVM swap partition, i.e.:

from something like:

RESUME=UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx

to something like:

RESUME=/dev/mapper/ubuntuvg-lvswap

After that,

sudo update-initramfs -u

Then restart and the problem was solved.