DHCP and multicast stop working when WAN DHCP is renewed

I have a very strange problem on 19.07.07 with both ArcherC50 and ArcherC7 where, for some bizarre reason, VIRTUAL GUESTS that send DHCP and multicast can no longer receive DHCP replies or IPv6 SLAAC/RA until either the WAP is rebooted, or I log in and restart the network service.

It occurs only after the eth0.2/WAN has its DHCP lease renewed. Even if I set the br-lan DHCP lease times to 5 minutes, they will work fine up until the eth0.2/wan interface has its DHCP renewed. At that point or shortly afterwards, any DHCP request sent by a virtual guest on any hypervisor that associates to the WAP are either ignored or formed in such a way that the guest never receives them.

Devices that access the wifi directly have no issues, I can release/renew DHCP on a laptop or mobile phone, however running guests in VirtualBox I can no longer receive DHCP or IPv6 from the router. Interestingly, I can see in the syslog the DHCPOFFER for the MAC of the virtualised guest, however I don't seem to receive them. Doing a wireshark on the hypervisor I don't see them either

I can reboot the hypervisor as many times as I want, it will never get DHCP for the guests unless I either reboot the openwrt WAP, or log in with a working device and restart the network service. Yet, the hypervisor itself or any device that is able to associate to the WAP has no issues whatsoever with DHCP. So without rebooting the openwrt router, I can restore DHCP and multicast service that way as well.

Any tips on how to troubleshoot this?