What about if I create the RI in forwarding mode, like that:
rib-groups { ISP1-to-ISP2 { import-rib [ inet.0 ISP1.inet.0 ISP2.inet.0 ]; } } forwarding-table { export LOAD-BALANCE; } } policy-options { policy-statement LOAD-BALANCE { then { load-balance per-packet; } } } routing-instances { ISP1 { instance-type forwarding; routing-options { interface-routes { rib-group inet ISP1-to-ISP2; } static { route 0.0.0.0/0 next-hop 192.168.13.254; } } } ISP2 { instance-type forwarding; routing-options { interface-routes { rib-group inet ISP1-to-ISP2; } static { route 0.0.0.0/0 next-hop 192.160.13.254;