Same issue here: it already took a long time for the previous issues to get fixed (firmwares after 1.0.2.8_1.0.45 broke IPv6, see reference below) but yes once again the poor support of IPv6 in RAX200 shows).
Using v1.0.10.140, on restart the RAX200 will properly make IPv6 operational to my devices but then it will suddenly stop and all kind of weird issue will happen since devices now need to fallback to IPv4 with a half working network: applies to both wired and wireless.
Now downgrading until I find which firmware broke IPv6...
Their was comments about this being due to Comcast/Xfinity poor networking but Comcast has been doing IPv6 it for a very long time...
