Seems you are right. Take a look here. Here’s what I found on the internet (no ad intended, just read the theory). Two things are on my mind - grounding and shielding, to either devices - contactor or W5500 assembly. It would be wise to do them to W5500 because then it will be secured from other EMI sources. As I said before IMHO most susceptible parts of W5500 circuit are (analog) jack with magnetics and RX/TX wires.
