I'm working on scenario mentioned in file attached:
R3 and R4 are PE routers, C1 and C2 are CE routers, rest are P-routers. OSPF is running in the core IGP. RSVP and MPLS tunnels are configured on all intermdiate interfaces.
18.104.22.168/32 and 22.214.171.124/32 are loopbacks of R3 and R4 and BGP peering is between loopbacks.
Problem is when I'm configuring explicit path (R3-R1-R2-R5-R4) in tunnel at R3, traffic is not passing between C1 and C2 thought tunnels are up. I noticed that MPLS forwarding table in R3 is showing Untagged in outgoing label for 126.96.36.199 prefix.
Similar setup is working fine if i configure dynamic tunnels (dynamic path is R3-R1-R2-R4) and I see Pop tag is showing as outgoing label for 188.8.131.52 prefix.
Attached file has tunnel and explicit path config, output of sh mpls forwarding and sh mpls traffic-eng tunnels.