Android devices cannot get an IPv6 address

[egc]

Late to the party but it looks like you have got a /64 PD.

From your other thread:

@OpnEnt

        "ipv6-prefix": [
                {
                        "address": "2600:1007:a012:78c7::",
                        "mask": 64,
                        "preferred": 26,
                        "valid": 36,
                        "class": "wan6",
                        "assigned": {
                                "lan": {
                                        "address": "2600:1007:a012:78c7::",
                                        "mask": 64
                                }

But you are using relayd?

If you only have lan then you can use that PD for your lan and you do not have to revert to relayd, me thinks