We are aware of a bug in JetBackup4 for cPanel where compressed backups for accounts that are using both MySQL and PostgreSQL fail to dump the MySQL backup for the affected accounts.
We have an internal GIT case JB4-#1831 to address this issue and have created the following patch which can be downloaded here:
Mysql & Postgresql compressed backup patch
This patch must be extracted then uploaded on your server and replace the following the file:
/usr/local/jetapps/var/lib/JetBackup/Cpanel/Backup/Databases.inc
Our apologies for the inconvenience caused and thank you for your understanding regarding this matter.