Hi @Lorimer As per our discussion here, the reason is highlighted
I think this is the first time NP ongoing maintenance is happening. There might be future reasons where hardware failure, or network device failure for the redeployment of nodes.
Thus NP wiki is getting improved with these learnings. Right now it is at its basically level of info for ongoing node maintenance https://wiki.internetcomputer.org/wiki/Changing_IPv6_addresses_of_nodes