I’ve had issues with the built in ethernet port on a couple different Ugoos AM6b+ (typically manifest as not acquiring an IP from DHCP, generally not passing packets reliably). However, in every case where I’ve used a USB-A → Ethernet adapter it has worked flawlessly and continuously.
I also have erratic behaviour with built in ethernet adapter (lowering transport speed while streaming) but only in CE. In Android it works perfect, never any glirch or speed drop.
In CE it sometimes boots with very low speed (20-30 Mbits on a 500Mbits fiber) I have to reboot it several times before it works with decent 350-400Mbits. On Android it always connects wth 450Mbits…
But, because of other reasons I regularly use WiFi, which works OK for my needs
Do you only have this problem on LAN?
Yes, as I wrote, when it connects to the router with 20-30 Mbit/s I also had problems with local streaming high-bitrate material, same as with internet streams. After restarting AM6B+ several times it finally connects to the router with decent speed; but never as fast as on Android, always at least 10% slower.
For other treasons I started using WiFi which works the same in CE and in Android, and satisfies my needs for speed, always above 400 Mbit/s.
My possibly uninformed theory is that something is not-quite-right with the dtb.img we use for the device as it pertains to the ethernet port.
I don’t know if this is related, but I’ve sometimes checked the debug output to see the cache fill level, and sometimes it is going at 100% for a long time, then suddenly starts going down. Once it hits zero, it either stays there for a while or starts filling up again right away. None of this has an effect on the actual playback. IIRC I have cache set at 512MB with adaptive rate. The actual maximum cache in this case is shown as 192MB in the debug output.