YUM Kernel install fails - no depmod, no initramfs, but installs kernel and line in GRUB (w/o initramfs)

• PURPOSE: Looking for troubleshooting assistance, trying to find the root cause
• SITUATION: I've now had a 2nd occurrence of this (among dozens of systems that upgraded just fine), and I cannot figure it out
• PLATFORM Red Hat Enterprise Linux (RHEL) x86-64 Workstation
• RELEASE: Release 6, Update 6 (installed) to Update 8 (upgrade via YUM)

As part of a YUM upgrade of systems from RHEL 6.6 to 6.8, using a local YUM repository (systems do not have Internet access), everything seems to install correctly, then the system is rebooted. It kernel panics, due to no initramfs and modules required to boot.

Upon further inspection, there are no module dependency files in /lib/modules/(version). So the fix is either ...

V=2.6.32-642.1.1.el6.x86_64
depmod -a ${V}
mkinitrd /boot/initramfs-${V}.img ${V}
vi /boot/grub/grub.conf  (add initrd line)

Or ...

V=2.6.32-642.1.1.el6.x86_64
rpm -ihv --replacefiles --replacepkgs kernel-${V}.rpm

Either will fix the issue, re-generating the module dependencies and a new initramfs with all required modules and their dependencies.

NOTE: Failure to run depmod first will create an incomplete initramfs (modules with missing module dependencies in the initramfs) that will still kernel panic.

Again, looking for any and all troubleshooting advice, trying to track down the root cause. This only occurs very infrequently, and I cannot find any differences between these systems that failed to have depmod/mkinitrd complete as part of the new kernel install, and those that worked just fine.