Same MAC on multiple network interfaces

I have a somewhat special setup where I have VMs that sometimes need to move between different networks/VLANs. I have used to add two DHCP reservations per MAC, one for each network. For example MAC A has both 10.0.10.55 and 10.0.20.55, so this VM is always available on 10.0.x.55, depending on if it is in VLAN 10 or 20.

This has worked flawlessly for a long time, but I've recently started having issues with this setup. I see that my VMs get an adress in one zone (10.0.10.55), but a gateway in another zone (10.0.20.1). Has there been a change to OpenWrt/DHCP packages recently that creates this issue? I know I probably just have to stick to one DHCP reservation per MAC moving forward...

As a test, have you tried to specify the gateway parameter for the host in the config too?