I've also hit this issue. I go round it by loading up a 18.04 Live USB in live mode. I then mounted my HDD onto the live OS (I only encrypted my home folder, so wasn't an issue). I then cded into the mount directory and ran `chroot ./`. Then added `size=256` to the end of the /swapfile line in /etc/crypttab and ran update-initramfs -u (hence the chroot).
I've also hit this issue. I go round it by loading up a 18.04 Live USB in live mode. I then mounted my HDD onto the live OS (I only encrypted my home folder, so wasn't an issue). I then cded into the mount directory and ran `chroot ./`. Then added `size=256` to the end of the /swapfile line in /etc/crypttab and ran update-initramfs -u (hence the chroot).