3.1.2 / routes disappear from kernel

[Alexander Javoronkov]

Greetings, I have stumbled on a problem with the new (v3) BIRD. I've been using v2 (still using 2.15.1 on old systems) over the years without problems.

The kernel4 protocol is defined with the following options:
* persist off; (I need the routes to exist only when the BIRD is running)
* scan time 86400; (BIRD v2 had a very hard time scanning Full View routing tables, so I have incremented this number)
* learn off; (I only need to export routes to the kernel)

// Disregard the full view comment, I am having a problem even with a simplest setup with 1 or 2 routes.

"birdcl show route export kernel4" shows that routes are supposed to be exported to the kernel:
10.0.4.0/24          unicast [users 16:43:23.752 from fe80::be24:11ff:fe00:303] * (100) [AS65004i]
	via 10.0.3.3 on eth1

However, when I check the routes (ip -4 r), they are not there.
If I run the "birdcl configure", the routes do not appear.
If I restart the protocol with "birdcl restart kernel4", I start to see the routes in the routing table.
Some time passes (something about an hour) and they disappear (without a single message in the logs).

Please advise how can I further debug/fix this problem.

LXC, CentOS 9 Stream, bird-3.1.2-1.el9.x86_64