Hi,
Since moving from 1.4.4 to 1.5.0 (ISC DHCP to Kea DHCP) I've been struggling with DHCP renewals not working properly. It seems that no Unicast DHCP renewal requests work, the are always NAK'd as follows:

Apr 09 01:18:09 kea-dhcp4[208553]: 2026-04-09 01:18:09.326 ERROR [kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001 [hwtype=1 6c:79:b8:ec:13:49], cid=[no info], tid=0x9eb95cf4: failed to select a subnet for incoming packet, src 192.168.0.152, type DHCPREQUEST
Apr 09 01:26:03 kea-dhcp4[208553]: 2026-04-09 01:26:03.573 ERROR [kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001 [hwtype=1 50:32:37:c4:fa:8c], cid=[01:50:32:37:c4:fa:8c], tid=0xd53ecc4e: failed to select a subnet for incoming packet, src 192.168.0.101, type DHCPREQUEST

This makes the clients fall back to a standard broadcast DHCP Request, which then works just fine.

After lots of debugging and posting to the Kea mailing list, a Kea developer has come back with the following message:

This is a VyOS-specific bug, which happens in this exact situation. VyOS 
is patching Kea to fix another issue, but the patch is incorrect. The 
patch was submitted to us here:

https://gitlab.isc.org/isc-projects/kea/-/merge_requests/2811

One of our developers noticed the problem, and there's a second commit 
in the MR which resolves it, but that has not been applied to VyOS's 
patch.  If you build VyOS yourself, you can update the patch or remove 
it if the issue it's fixing doesn't apply to you.

-Doug

This is quite an impactful bug, as it causes interfaces on Apple Mac devices to temporarily drop their IP sessions while the "full" DHCP renewal is underway. This causes VPN sessions to drop etc.