Hey, 

I've migrated from 2.16.1 to 3.0.1 and I'm facing some issues with the BMP protocol. 
The TCP session goes up but I don't receive all peers up notifications. I receive some (but not all it seems) when I restart bird after have started my BMP collector. If I do the opposite, I get none.

Also, I don't receive route monitoring messages. To be precise, I receive only one route monitoring message when I receive a peer up notification. But this one is empty (meaning no announced/withdrawn prefixes in it). Also I receive it just just before the peer up, which is a bit weird. I should receive a tons of them, with announced prefixes in it, right after the peer up. 

Here is my BMP configuration: 

protocol bmp {
    station address ip 2a06:de00:50:cafe:100::c port 4000;
    monitoring rib in pre_policy;
    monitoring rib in post_policy;
}

bird> show protocols all bmp1
Name       Proto      Table      State  Since         Info
bmp1       BMP        ---        up     18:08:26.528  Established
  Created:            18:08:16.105
  Station address:    2a06:de00:50:cafe:100::c
  Station port:       4000
  Pending TX:               0  B (limit 1024.0 MB)
  Session TX:             789  B
  Total TX:               789  B

Do you experience the same behavior?
Please let me know if you need more information, I'm happy to make some other tests if needed.

Best,
Matthieu.