Luckily I had a good node that upgraded to 4.2.5.1 successfully - so I duplicated the
mount as:
mount -t ext4 -o rw,relatime,seclabel,discard,stripe=16,data=ordered
/dev/mapper/onn-var_crash /var/crash
Then removed the two 4.2.5.1 Logical Volumes.
Then yum reinstall ovirt-node-ng-image-update-4.2.5.1