hmm, ive heard reports about ai difficulty to navigate the bridge, hmm, seems weird. maybe dont use waypoints???
you might have better luck if you use the "move" command.
put a game logic on the beach where you want the bmp to enter name it move1 make another on the other shore, make it move2.
in init line, put "bmp1 domove getpos move1
make a trigger, in conidition, put (bmp1 distance move1) <= 5
on activation, put "bmp1 domove move2"
put a trigger with condition (bmp1 distance move2) <= 5
make this trigger a switch.
give the bmp a waypoint somewhere in the objective area (city on other side of bridge) and drag a "syncroniztion line fromt the waypoint to the trigger mentioned above.
this method might work, im not sure though