A PD length of /64 is broken. Here is why:
When mapping out the addresses, please allocate for /48, but hand out a /56 by default
Best Current Operational Practice for Operators: IPv6 prefix assignment for end-users - persistent vs non-persistent, and what size to chooseAssigning a /64 or longer prefix does not conform to IPv6 standards and will break functionality in customer LANs. With a single /64, the end customer CPE will have just one possible network on the LAN side and it will not be possible to subnet, assign VLANs, alternative SSIDs, or have several chained routers in the same customer network, etc.
When mapping out the addresses, please allocate for /48, but hand out a /56 by default