Try to add static arp entry on R4 ge-0/0/0:
set interfaces ge-0/0/0 unit 0 family inet address <R4-IP> arp <R2-IP> mac <R2-facing-interface-mac>
Try to add static arp entry on R4 ge-0/0/0:
set interfaces ge-0/0/0 unit 0 family inet address <R4-IP> arp <R2-IP> mac <R2-facing-interface-mac>