ORA-12514 while tnsping works okay

I have a 2-node 12cR1 RAC cluster that has been running great. Last Friday we replaced our juniper firewall with palo alto firewall, then I rebooted the RAC nodes. When I tried to start up my application server, it failed to start. I then noticed I couldn't connect to my database with error of ORA-12514, even though tnsping works fine. Initially we thought the firewall change might have broken it because all was working great before the firewall change and server reboot. However, since tnsping works fine, it means there is nothing blocking the application server from reaching to the database through the defined port. puzzles. puzzles. Then I noticed the remote_listener parameter was empty, which led me to look at sqlnet.ora file, and found EZCONNECT was no longer configured in NAMES.DIRECTORY_PATH. At this point, I remember that I copied a set of sqlnet.ora and ldap.ora file from a different server so that I can use LDAP to replace tnsnames.ora file for database services repository a few weeks ago. Apparently this new sqlnet.ora file doesn't have EZCONNECT configured in it. It didn't break anything until the RAC nodes rebooted, which coincided with the firewall change.