I'm unaware of WHM showing these. They are typically in cPanel > Forwarders area instead of WHM.
The files that house the forwarders are /etc/valiases in root SSH and each domain has a file there.
You might try running this command in case the issue is being caused by improper permissions:
If that doesn't work and you aren't seeing any forwarders listed in the files in question, you can check your backups if you are saving the configuration files and have WHM > Backup > Configure Backup enabled. These would be in /pathtobackup/cpbackup/daily|weekly|monthly/dirs/_etc_valiases
Of note, please replace
pathtobackup with the path to the backup, and select daily, weekly or monthly for the folder to check.