Basically the DNS request contains a host name of which the label is longer than 63 characters. A "label" is any component between dots in a host name.
In the case of the ASA, the DNS enforcement reads the domain name one label at a time. According to RFC 1034, a label is zero to 63 octets in length.
So the ASA behavior is the expected one,
You cannot tune the DNS inspection to increase the label size, so if you are 100 % sure this is valid traffic you could (NOT recommended) disable the DNS protocol-enforcement which will basically ignore what the RFC says (Again not recommended)
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...