Disable universal plug and play on all nodes within each network, except one. As discussed here: Farming on multiple computers, upnp on? - #5 by codinghorror
There could be many reasons - besides upnp - why your farms fail to earn a coin. Could be other technical issues (slow nodes, poor synchronization) or just bad luck.
The best thing you can do is join a pool (with NFT plots) and start watching stats: what is percentage of valid proofs over 24 hr period VS stale/invalid. Generally if you get 99%+ valid, nothing to worry about.
Also I am curious how the nodes will show up in the pool if they were initialized with the same keys. Definitely try running at least 2 nodes off the same network on a pool and see if there is any conflict. They should show up either as 2 separate “farmers” or one big farmer with appropriate estimated size