One more thing to try, would be disabling RSTP on the bridge. see DHCP client on bridge does not work? - #3 by 2frogs However this was from a dhcp client on the bridge, not for a down stream device. This is mostly last resort change that I can't explain why it should work, but it may be worth trying to see if if makes any difference.
It is a really odd problem because:
- ubuntu works when directly connected to ASUS
- windows works through hap lite, but ubuntu does not. (and the bridge should be "transparent", i.e. it isn't configured for dhcp snooping).
Has your config changed since the last posted config?
Are you still "cloning" the mac address of the ubuntu host on the bridge? If so I would reset to the original, because when in bridge mode, it does seem is would cause the bridge confusion (duplicate macs).
This is an odd problem, it seems that you have demonstrated that the ASUS dhcp server does work with the ubuntu host. Have you verified that the other adapters on the ubuntu machine can also get in ip address when directly connected to the ASUS. Have you verified that the ubuntu can obtain in IP with both cables involved (one at a time)? Just to verify that cables are working.
Does the ASUS router have Gb ports? That's one diffenence. If the ubuntu ethernet adapter won't auto negotiate with the 100 Mbps on the hap mini. But that doesn't seem to make sense either based on the top right screen in Screenshot 2025-11-29 at 18.48.39, which shows R (running) and traffic for ether1 ether2 and wlan1.
Edit: I see that you found another host that does work.
About the only option at this time would be to load wireshark on your ubuntu and capture traffic. Perhaps compare to tool/sniffer on the hap lite (but hw offload must be disabled). I have never tried using sniffer when configured as a bridge only, so perhaps it works differently than when running as a router.
Do you have a usb to ethernet adapter you could try with the ubuntu server? It really seems odd that none of the servers adapters are able to get ip addresses. Are you the ubuntu interfaces are correctly configured to use dhcp?