On a multi-boot machine the big question is “who controls the boot process”.

My “big box” has two SSD (Ubuntu, CentOS) a 1T HDD (eight Linux partitions if memory serves) and a small clunky HDD with W7.

In this case I choose Ubuntu to control the boot process and understand that if I update the Kernel in any of the other distros I will not be able to boot to it unless I run update-grub (Ubuntu script similar to your mkconfig command) which will look at all the partitions and disks to boot to the most recent first.

Likely CentOS is your current control and it likely uses an older grub.

Choose a recent “grub2” distro and make it your “boot control”.