"show route protocol bgp hidden extensive " will display the hidden routes and the reason each of them went hidden.
There can be many reasons. Predominantly it might be due to next hop not reachable . Check your next-hop-self policy,if you had got the routes advertised from an IBGP speaker/peer..
You can also try " show route advertising-protocol bgp <neighbor-address> hidden" if you want to see hidden routes
specific from a neighbor
"show route hidden " will also displays the hidden routes
Please marked this as accepted solution, if it solves the problem.