then pushed that snapshot to a new WP 18.04 droplet.
With simple Droplets, all you need to do with a snapshot is Create Droplet from it. You can do the same with Wordpress but a few configs need to be updated after the restore onto a new IP / host / url. To clarify, theres' no need to create a WP 18.04 and then restore, the snapshot is a full restore. Assuming that's what you meant, then the config to be updated for Wordpress moving to a new IP address and new host is found in the wordpress db in the wp_options table. Those must be updated.
Following this article I've done that to one Wordpress Droplet recently, using these steps; https://stackoverflow.com/questions/535534/wordpress-host-ip-changed
–Get the root mysql password
more /etc/apache2/sites-enabled/000-default.conf .digitalocean_password
–Connect to the database
mysql -u root -p
<enter the password from above>
change to the wordpress db
–Check the wpoptions for siteurl and home
mysql> Select * from wp_options where option_name IN('siteurl','home');
–Update those to my new values
update wp_options set option_value='http://example.com' where option_name = 'siteurl';
update wp_options set option_value='http://example.com' where option_name = 'home';
–Restart the Droplet, wait a few minutes for it to come up, and the site should be up and running on your new host.