Good. Now we can continue.
Internal test shows, that tag was setting correctly (output from another router from same OSPF area):
vyos@vyos:~$ show ip ospf route
============ OSPF network routing table ============
N 10.99.5.0/24 [1] area: 0.0.0.0
directly attached to eth1
============ OSPF router routing table =============
R 10.99.5.11 [1] area: 0.0.0.0, ASBR
via 10.99.5.11, eth1
============ OSPF external routing table ===========
N E2 10.11.12.0/24 [1/20] tag: 20570
via 10.99.5.11, eth1
If in your environment this not working, then show please your complete configuration of both routers (10.99.5.11 and OSPF receiver) and we will try to see what can be wrong.
Also, please show outputs of this commands:
show ip ospf database
show ip ospf neighbor
show ip ospf route