I think everyone now what is a RIB-Failure in BGP context. It sounds obviously as an exact same route with a lowest AD as {e|i}BGP. We have VRF-Lite on R1 here :

We have :

1#show ip bg vpnv4 vrf CUST
BGP table version is 11, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
              x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 65001:1 (default for vrf CUST)
 *>  10.1.1.1/32      12.0.0.2                 0             0 65002 ?
 *>  10.2.2.1/32      12.0.0.2                 0             0 65002 ?
 r>  10.3.3.1/32      12.0.0.2                 0             0 65002 ?
 r>  10.4.4.1/32      12.0.0.2                 0             0 65002 ?
 r>  10.5.5.1/32      12.0.0.2                 0             0 65002 ?
 r>  10.5.5.5/32      12.0.0.2                 0             0 65002 ?
 r>  10.6.6.6/32      12.0.0.2                 0             0 65002 ?
 r>  12.0.0.0/24      12.0.0.2                 0             0 65002 ?
R1#
R1#show ip route vrf CUST

Routing Table: CUST

Gateway of last resort is not set

      10.0.0.0/32 is subnetted, 2 subnets
B        10.1.1.1 [20/0] via 12.0.0.2, 00:37:49
B        10.2.2.1 [20/0] via 12.0.0.2, 00:37:49
      12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        12.0.0.0/24 is directly connected, Ethernet0/0
L        12.0.0.1/32 is directly connected, Ethernet0/0
R1#

So the only route we can have a RIB-Failure due to lowest AD is : 12.0.0.0/24. What is the problem with others ?
We can know this by using :

R1#show ip bg vpnv4 vrf CUST rib-failure
  Network            Next Hop                      RIB-failure   RIB-NH Matches
Route Distinguisher: 65001:1 (default for vrf CUST)
10.3.3.1/32        12.0.0.2                      Route limit              n/a
10.4.4.1/32        12.0.0.2                      Route limit              n/a
10.5.5.1/32        12.0.0.2                      Route limit              n/a
10.5.5.5/32        12.0.0.2                      Route limit              n/a
10.6.6.6/32        12.0.0.2                      Route limit              n/a
12.0.0.0/24        12.0.0.2            Higher admin distance              n/a
R1#

The problem is :

ip vrf CUST
 rd 65001:1
 maximum routes 4 80
!

You know surely now why it is in ‘RIB-Failure’ state…