Strange, I can not confirm this. I was curious and gave RC6 (r28388-58d0057481) a test run on my NanoPi R4S. Everything works normal, LAN port is up and running without any problems.
We discussed this here a couple of times already. The R4S seems to be a bit "picky" when it comes to power supplies and also SD cards. I for example recently had issues booting from SD cards that actually worked before. I then used a different one and everything worked again ... it actually looks like the LAN port does not come online, but actually I believe the device does not boot at all ... unfortunately never had time to connect an UART cable and take a deeper look.
Can you try a different SD card?