Netflow records with Destination Ports 1025,257 and Protocol as ipv6-icmp

I have some Netflow records from a bunch of routers. The records contain IPv6 flows and there are entries with protocol as ipv6-icmp and their destination port values as 0, 1025 and 257. I know from this link that the value of 0 for ipv6-icmp in netflow indicates an echo reply. Is there any resource to find the meaning of the ipv6-icmp-1025 and ipv6-icmp-257?

ICMP and ICMPv6 do not have port numbers. Possibly netflow is using 0 to indicate this is not a UDP or TCP flow.

Standard types and codes are in IANA registries. In v6, type 0 actually is reserved, and would be invalid on the wire. And as these are 8 bit fields, they only go up to 256.

These do not map obviously to ICMP. Possibly some other logging or packet capture would be better at analyzing it.