Ok its fixed. I think there are a few things at play here.
First, I think the system ran out of space because the boot volume is quite small, and then this caused the ifreload package to glitch. In typical fashion there were kernels going back...
I have a 3 node cluster. I updated the first one & rebooted, went smoothly. Then I went to update and reboot the second, but it wouldn't boot up:
VFS: Unable to mount root fs on unknown-block(0,0)
I rebooted and went into advanced options, and...