Is the MTU on everything on your network set to 1500? It may be settable on your computer and the router. It’s fixed to 1500 on the My Cloud.
eth0 Link encap:Ethernet HWaddr 00:90:a9:f6:46:0c
inet addr:172.16.0.148 Bcast:172.16.0.255 Mask:255.255.255.0
inet6 addr: fe80::290:a9ff:fef6:460c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2480554 errors:0 dropped:0 overruns:0 frame:0
TX packets:1572555 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:571837689 (545.3 MiB) TX bytes:469083855 (447.3 MiB)
The above is what the LAN port on my My Cloud NAS is set to. Will be the same for you.
I’ve has an issue when I enable an MTU higher then 1500 then wiered comms works and WiFi comms fails.
It’s one cause that would cause the issue you’re experiencing. I can’t see it being WiFi isolation. That simply prevents WiFi devices talking to each other.
Just one extra thing. Sometimes when unplugging the network cable the WiFi could be disconnected and needs reconnecting to the WiFi network?
I don’t gave any experience with the BTHH4.