@biomesh how would I tell if mid split is enabled? I had a working config for a while getting the default route via DHCP, then suddenly stopped working (could no longer connect to the gateway it was setting). So I just followed the advice of @tangent and turned on RA instead, but there was no default route set. If I set ::/0 to %ether1 manually, everything works fine.
The only other difference I have is that I’m using a hint to request (and get) a 60-bit prefix. Not sure if that would muck with the RA though.