Hi ironypirate,
just saw this post now.
I was able to have the setup you mentioned working.
I have connected my unify udm (dream machine) port 5 (WAN) to the 10G LAN of the Sunrise Fiber router. IPv6 Disabled. All works as expected.
Let me know if you need any info on the setup, since the “support” team is not even able to help with their own equipments.
cheers
joao quintas