Is your Windows station connected to a port with multiple VLANs configured? If yes, you may be seeing the issue with Windows stripping the VLAN tag from packets and applying RAs from all the VLANs. Windows require a port with single untagged VLAN and no tagged VLAN to operate correctly.
Some drivers allow for VLAN configuration that really works (in other words, only use the one configured VLAN and drop traffic from all other ones), but most drivers fail in this job and simply let all packets through.
In the IPv4 world the issue was hidden because the outgoing traffic is typically untagged, so the DHCPv4 exchange (which is initiated by the client) is only performed on the untagged VLAN. RAs are sent by the router and multicasted to all the stations on the VLANs and that’s why we see the issue now.