I am guessing the gear mechanism is not reversing. It is supposed to turn right for a while (a few minutes) then go neutral, then turn left, etc.

To test, hang the Navigator in the pool so that the feet are not touching (e.g. just a foot into the water) and watch the rotation. You should see it cycle left-right-left.... If it is turning in just one direction, that is your problem. Cleaning it may work, but it probably will require a new gear box.

Sometimes it will stop because of small blockages in the feet that cause it to turn only one way (which is why you want to do the above test whiel suspended freely). Clean out any debris, and check for freedom of movement in the bearings on the A-frame. If you're lucky, it will be something that cleaning will fix.