Nimbostratus
NimbostratusI'm currently working with this iAPP in an 11.4 lab environment. The iAPP works by using a unique local IPv6 address (FDF5::{vip_address}) as a sort of "loopback" for the packet replication. If you haven't configured unique local IPv6 networking in your environment, you'll experience the symptoms you describe as the first iRule doesn't have a valid IPv6 network to forward the "distribution" packet through.
As a work-around, try adding an arbitrary address in (FDF5::/64) to the same interface as the primary application VIP. It worked to resolve similar issues in my lab environment, both the second VS node monitoring, and the actual forwarding of packets.
I'm considering updating the iAPP to change the "distribution" VS to the link-local range as a potential fix, rather than having to add an address from the designated unique local range.
The port problem on the second "distribution" VS you describe might be only cosmetic, as long as the pool member of the primary VS pool matches the address&port of the secondary VS VIP, AND the F5 has a valid way to forward the IPv6 packet, you should be able to monitor the VS and get forwarding working.
Look at the Virtual Server statistics to verify that the traffic is making it from the first VS to the Second VS. You should see input traffic for both VS objects if the IPv6 forwarding is working.
Let me know if adding an arbitrary IPv6 address works for you in test.