There has been a noticeable lag in my terminal whenever I’ve tried to run a command with
sudo. Basically you have to wait 5 seconds and then the password prompt finally appears.
It turns out this happens if you change the hostname of the machine from its default. For me this would have happened during installation. Editing the /etc/hosts files to include my laptop’s hostname  now ensures that running commands with
sudo is instantaneous. For example, something like
sudo echo 127.0.0.1 $(hostname) >> /etc/hosts should work (but don’t just copy/paste that).
My /etc/hosts file was empty, btw. I don’t know if the standard localhost mappings are now defined somewhere else and I’m supposed to be editing a different file these days, but the above worked fine so I’m leaving it.
Posting this here in the hope that the PureOS devs might program this fix into the distro.