Our jobs are configured with 'Email Notification' checked and 'Send e-mail for every unstable build'

All failed subversion and mercurial jobs have this at the bottom:
"An attempt to send an e-mail to empty list of recipients, ignored."

The jobs were started by polling scm, and the 'Changes' does list the correct username of the person who made the change.

This happens on m2 job types as well as regular jobs. It happens on both the slaves and on master. I listed the component as core because it happens with both mercurial and subversion.

The last time I updated it was from version 1.403, and email notifications worked then (the configuration under 'Manage Jenkins' should be correct)

It seems the list of people who made changes isn't getting passed from the scm plugin to the email section. I do have the Email-Ext plugin installed, but not configured, on these jobs.

What can I try next? I didn't see any fixes in the recent changelog related to email, or I'd try updating. I'll start experimenting, but hoping someone here is aware of the bug and a possible fix.