cryptsetup warning message about swap file
Solution 1:
It's a result of this bug:
https://bugs.launchpad.net/ubuntu/+source/cloud-initramfs-tools/+bug/1720036
It seems to just be an slightly irritating error message with no practical consequences and is safe to ignore
Solution 2:
After this warning the next boot fails. While booting, the system is waiting for the encrypted swap file, but unsuccessfully. After a while a command prompt appears. For the normal boot the "exit" command have to be issued.
Solution:
sudo swapoff -a
sudo update-initramfs -c -k all
sudo swapon -a