If your relay is configured with an IPv6 ORPort:
ORPort [IPv6]:Port
and it is not reachable over IPv6, it will be excluded from the consensus.
This can happen if the address is wrong, or the IPv6 routing is wrong.
If your relay isn't in the consensus, it will log warnings.
Or, you can check Relay Search at:
If your relay is not Running, you can check the votes for your relay here:
If all the authorities don't vote for your relay, it has a tor or IPv4 problem.
If a few do vote Running, it probably has an IPv6 problem.
(If you want to be sure, check which authorities support ReachableIPv6
in the consensus health Known Flags table.)