IPv4 BGP prefix lists does not seem to be properly enabled in FRR. IPv6 does not seem to have the same issue.
Version: VyOS 1.2.0-rc5
VyOS config:
set policy prefix-list test rule 10 action 'permit'
set policy prefix-list test rule 10 le '24'
set policy prefix-list test rule 10 prefix '100.140.22.0/23'
set protocols bgp 1 address-family ipv4-unicast redistribute connected
set protocols bgp 1 address-family ipv4-unicast redistribute kernel
set protocols bgp 1 neighbor 1.1.1.2 address-family ipv4-unicast prefix-list export 'test'
set protocols bgp 1 neighbor 1.1.1.2 address-family ipv4-unicast prefix-list import 'test'
set protocols bgp 1 neighbor 1.1.1.2 remote-as '2'
FRR generated config, notice the missing prefix-lists.
vtysh#
router bgp 1
neighbor 1.1.1.2 remote-as 2
!
address-family ipv4 unicast
redistribute kernel
redistribute connected
exit-address-family
!
Adding the prefix-lists manually to FRR makes things work as expected.