Hi,u need to assign  the new adress in corresponding Logical Node Profile of the IPN L3-Out: go to "Tenants -> infra -> Networking -> "IPNL3Out" -> Logical Node Profiles -> "NodeX" and change the loopback adress 

Actually had the same problem after upgrading to 6.1(2g) and also assigned a different IP to one of the spines

u can use linux commands e.g "watch show interface ethernet 1/1"

Hi @JamesB11 ,Did u already check your discovery mode settings? (can either be "strict" or "permissive")System->Controllers-> APIC1 --> Cluster as Seen By Node regards

I think you´re misunderstanding the function/need of L3 Outs.  L3 Outs are dedicated routed interfaces which are (or can be) used to connect routed aci networks & external routers, firewalls,etc.You only need L3 Outs if you plan to migrate SVIs/DGWs ...