S97 and S57 have direct route.
please try S97 and S57 configure the follow command to form ldp session. and configure the connected interface mpls ldp.
[PE1] mpls lsr-id 1.1.1.9
[PE1] mpls
[PE1-mpls] quit
[PE1] mpls ldp
[PE1-mpls-ldp] quit
[PE1] interface gigabitethernet 3/0/0
[PE1-GigabitEthernet3/0/0] mpls
[PE1-GigabitEthernet3/0/0] mpls ldp
[PE1-GigabitEthernet3/0/0] quit
the same configure command in S97 and S57. and check use command "display mpls ldp session"