The IPv6 addresses that were assigned in SolusVM are not manageable in Wyvern but they are still routed to your VPS. Wyvern does not use the "shared /64 block" method that SolusVM did and assigns each client a /64, which is the correct method of allocation, so it's not possible to import the old IPv6 addresses into Wyvern without a complete re-write of the control panel. We can assure you that your old IPv6 addresses do still route to your VPS and will continue to route to it in the future but rDNS and bandwidth counting are disabled for them.
The rDNS for old IPv6 addresses from SolusVM cannot be edited so please generate a new IPv6 address in Wyvern if you need this feature.