Topology is:
[cisco NCS5500 XR]---{gigabitethernet}---[CCR2004]==={L2TPs}===[Spokes]
CCR2004 is the LNS as of now, later would be CCR2116.
I tried OSPF and RIP as IGP without success. There are 5 Spokes on LNS/HUB. All the five LDP adjacency is DOp (D - DYNAMIC; O - OPERATIONAL; p - PASSIVE), but some of Spokes’s LDP remote bindings are inactive:
[oreggin@lns.mtik-test] > /mpls/ldp/remote-mapping/print where dst-address~"10[.]4"
Flags: I - INACTIVE; D - DYNAMIC
Columns: VRF, DST-ADDRESS, NEXTHOP, LABEL, PEER
# VRF DST-ADDRESS NEXTHOP LABEL PEER
714 D main 10.43.69.254 10.3.3.254 impl-null 10.43.69.254:0
716 D main 10.43.54.126 10.3.3.252 impl-null 10.43.54.126:0
718 D main 10.43.0.126 10.3.3.250 impl-null 10.43.0.126:0
720 ID main 10.44.27.126 impl-null 10.44.27.126:0
722 ID main 10.44.2.254 impl-null 10.44.2.254:0
From XR box, the last two Spoke are not pings. LDP remote binding shows those doesn’t have resolved nexthop(?) 
But they have:
[oreggin@lns.mtik-test] > /routing/route/print where dst-address~"10[.]4.*32"
Flags: A - ACTIVE; o - OSPF, a - LDP-ADDRESS, l - LDP-MAPPING; H - HW-OFFLOADED
Columns: DST-ADDRESS, GATEWAY, AFI, DISTANCE, SCOPE, TARGET-SCOPE, IMMEDIATE-GW
DST-ADDRESS GATEWAY AFI DISTANCE SCOPE TARGET-SCOPE IMMEDIATE-GW
Ao 10.43.0.126/32 10.3.3.250%<l2tp-user@realm-4> ip4 110 20 10 10.3.3.250%<l2tp-user@realm-4>
aH 10.43.0.126/32 ip4
lH 10.43.0.126/32 ip4
Ao 10.43.54.126/32 10.3.3.252%<l2tp-user@realm-3> ip4 110 20 10 10.3.3.252%<l2tp-user@realm-3>
aH 10.43.54.126/32 ip4
lH 10.43.54.126/32 ip4
Ao 10.43.69.254/32 10.3.3.254%<l2tp-user@realm-1> ip4 110 20 10 10.3.3.254%<l2tp-user@realm-1>
aH 10.43.69.254/32 ip4
lH 10.43.69.254/32 ip4
Ao 10.44.2.254/32 10.3.3.253%<l2tp-user@realm-2> ip4 110 20 10 10.3.3.253%<l2tp-user@realm-2>
aH 10.44.2.254/32 ip4
lH 10.44.2.254/32 ip4
Ao 10.44.27.126/32 10.3.3.251%<l2tp-user@realm> ip4 110 20 10 10.3.3.251%<l2tp-user@realm>
aH 10.44.27.126/32 ip4
lH 10.44.27.126/32 ip4
MPLS forwarding table:
[oreggin@lns.mtik-test] > /mpls/forwarding-table/print where prefix~"10[.]4"
Flags: L - LDP
Columns: LABEL, VRF, PREFIX, NEXTHOPS
# LABEL VRF PREFIX NEXTHOPS
3 L 19 main 10.43.69.254 { label=impl-null; nh=10.3.3.254; interface=<l2tp-user@realm-1> }
5 L 18 main 10.43.54.126 { label=impl-null; nh=10.3.3.252; interface=<l2tp-user@realm-3> }
7 L 17 main 10.43.0.126 { label=impl-null; nh=10.3.3.250; interface=<l2tp-user@realm-4> }
The same shows when I use RIP as IGP. The IPv6/VPNv6 is works like a charm and stable. On IPv4, it is totally random which Spoke can communicate with the XR and which can’t. Sometimes all of the Spoke have right LDP binding and mpls forwarding table entries, sometime neither, sometimes just the part of them. Any ideas?
Thanks!
oreggin