Comment 63 for bug 1872118

First I reverted isc-dhcp-server back to the original focal version, since I had an updated version from the PPA:
$ sudo apt install isc-dhcp-server=4.4.1-2.1ubuntu5 isc-dhcp-common=4.4.1-2.1ubuntu5

Then I install the update packages:
$ sudo apt update
$ sudo apt install libdns-export1109/focal-proposed libirs-export161/focal-proposed libisc-export1105/focal-proposed
$ dpkg --status libdns-export1109 libirs-export161 libisc-export1105 | grep Version
Version: 1:9.11.16+dfsg-3~ubuntu1
Version: 1:9.11.16+dfsg-3~ubuntu1
Version: 1:9.11.16+dfsg-3~ubuntu1

Then I restarted dhcpd:
sudo systemctl restart isc-dhcp-server

It has been running for four hours on both systems.