exportfs non-zero exit code without error message

Ubuntu Server 18.04, upgraded from 16.04, upgraded from 10.04. /etc/exports had things like

/path hostname(rw) 10.212.1.9(rw)

where the ip is for that hostname and all was fine, even when DNS wasn't working.

something seems to have changed since first upgrading to 18.04 where exportfs -r gives what appears to be a warning "duplicated export entries", but has now has a non-zero exit code, which causes the server to not start.

even with -v this still looks like a warning, it does not say anything about the exports not being applied or any hint that the processes was considered a failure.