Comment 3 for bug 1843507

I experienced the same issue.

cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.3 LTS"

uname -sri
Linux 5.0.0-27-generic x86_64

Machine would no longer boot successfully, primarily due to NetworkManager failing.
These are the steps I took to revert until resolved:
Boot in recovery mode, get to command prompt
dhclient <eth>
wget http://mirrors.kernel.org/ubuntu/pool/main/libi/libidn2/libidn2-0_2.0.4-1.1build2_amd64.deb
dpkg -i libidn2-0_2.0.4-1.1build2_amd64.deb
reboot
---
Note: If you have i386 libs you have to revert them as well:
wget http://mirrors.kernel.org/ubuntu/pool/main/libi/libidn2/libidn2-0_2.0.4-1.1build2_i386.deb
dpkg -i libidn2-0_2.0.4-1.1build2_i386.deb