I had the problem that updating Fedora installed a new kernel but the system never booted the new kernel. The reason is that grub2 does not reflect the changes.
To fix the problem, you simply have to execute the following command as root to obtain the grub2 configuration utilities and update the grub configuation:
dnf install grub2-tools grub2-mkconfig -o /boot/grub2/grub.cfg
Fedora should now boot again with that latest installed kernel.