I've moved up to the ER707 from Edgerouters.

On 3 different networks, all worked previously with varying configs previously, 2 are working fine using IPv6 in passthrough.

I have one domain that has IPv6 and for the life of me, I'm have zero success...

It's Comcast with a /56 and I typically would use /60 and it would work fine.  With the ER707, no luck. 

Here's a basic overview. IPs altered.  

Comcast gateway:

2603:xxxx:266:1100:xxxx:c3ff:fea3:xxxx

On my router it would get a WAN side IP

LAN side IP

2603:xxxx:266:1160:xxxx:xxxx:xxxx

Which I'd take and assign a static IP to the server
2603:xxxx:266:1160:xxxx:xxxx:200  

I'd simply use the LAN side IP of the router as the gateway and have the server issue IPv6's internally and everything just worked ... at least on the Edgerouter.  

Any direction would be appreciated.