The most common reason for this problem is having a filter policy applied to the redistribution statement, which denies the networks in question.
Another possibility is that the router has the auto-summary command enabled under the Border Gateway Protocol (BGP) configuration. The only routes in the routing table are the subnet routes. In this case, the only route advertised is the summary route.
To resolve this issue, perform one of these options:
Ensure that there are no filter policies applied with the redistribute command. These filter policies may be denying the networks in question.
If you require the subnets to be advertised, ensure that the auto-summary command is not enabled under BGP configuration. The auto-summary command is enabled by default. To disable it, issue the no auto-summary command.