Slack handles in Scheduled reminders

[jschenz-chwy]

I have set up a scheduled reminder for my team so that we can see any open PRs for repos our team is admin on each morning in our primary slack channel. For two team members (me and one other), we can see that our GitHub username is replaced with our Slack handle in the "waiting on" list; for others, it stays as their GitHub username.

Is there some configuration needed so that each of us will have our GitHub handle translated to our Slack handle?