I’m sure there are situations involving power supply noise contamination of the Ethernet signal, issues between routers and DACs, etc. Some setups are more resilient. I think my MSB system, with Digital Director and Renderer is sufficient at filtering anything but an actual fraudulent Ethernet implementation.
That being said, there are all sorts of things that apparently sneak through the transformer coupled, asynchronous Ethernet connections. Most are solved with an optical link somewhere near the rendering computer.
Lots of pundits, and sellers. We all have different system/issues. Auditioning is required, in my opinion. Before I got the Digital Director, I could tell the difference in my system when I used the UpTone Audio EtherRegen and the optical segment. (Even using generic SFPs) vs plain hub with copper Ethernet only.