Troubleshooting Merge Tag Issues in Email Automation

Anyone having issues with merge tags? I have an automation that sends an email to subscribers and the merge tags used to work. I don't know exactly when the issue started for me, since it's an automation that hasn't sent an email, yet. I tested to make sure the email worked as expected before activating the automation two months ago, but I went to test it again today since it's ~2 weeks before sending its first email to a subscriber, and it's not working anymore