annoying log, received route with strange next hop, Netlink File exists

Classified as: {Hitachi Rail - Public} Basically configured bird as below protocol device { scan time 10; } protocol kernel { scan time 10; learn; ipv4 { export filter XXXX; } } bgp and bfd are established, everything is fine. But only have some annoying log: Every 10 seconds to print below bird log, assuming this is caused by kernel protocol scan time 10. But why Netlink : File exists, it would write to kernel ??? KRT: Received route xx.yy.zz.0/24 with strange next-hop 10.0.0.1 Netlink: File exists Chris {Hitachi Rail - Public}