A router server is indeed what I imagine as the most likely way to get the same failure mode as what I saw with OSPF.
It's technically possible to verify that neighbor discovery works for the next hop that you receive from a route server. How to actually implement it depends on the underlying platform and could be complicated.
What did you verify on the data path? The traceroute command I tried failed before the packet reached the data path from 2a00:1098:2::7 to the next hop.
