I see. Just a suggestion you can confuse other forum members (yes, I’m frequently in that catagory ) with acronyms and miss out on good feedback concerning your problem.
If you’ve changed ports on your router and the cable and still see the issue it may be an internal router setting or possibly an Apple TV Ethernet port going away.
Same problem with cable with VLC also(SMB/FTP), other services over internet works fine. So for me is a brainstorm to get the reason. I guess problem can be at router settings…
Is it possible you have the Apple TV set up for network guest with internet access but not for LAN file sharing on the Ethernet MAC address but full privileges for the WiFi MAC address??
Finally done. At router settings Link aggregation and Spanning tree protocol(no idea what is it) was on, I’ve disabled it so right now no problem with cable.
Link aggregation was probably combining your ports into one (good for doubling bandwidth with multiple network cards or for failover). Spanning tree you could probably leave on but won’t need unless you add another switch. Spanning tree prevents network loops in home environments.