I found the addition of the 18.04 libnss-resolve package fixed my (intermittent) problems with name-resolution failures. Earlier comments indicate this package was not installed. The installation alters the nsswitch.conf file's hosts line to add "resolve [!UNAVAIL=return]" before "dns".
I found the addition of the 18.04 libnss-resolve package fixed my (intermittent) problems with name-resolution failures. Earlier comments indicate this package was not installed. The installation alters the nsswitch.conf file's hosts line to add "resolve [!UNAVAIL=return]" before "dns".