Sounds like the Polaris is being disturbed by the other jets. It's pretty sensitive to any other movement in the water. It relies on alternating shooting jets.
Alternatively, the mechanism inside can get out of whack and some jets aren't running correctly. The Polaris should alternate among all its jets, but it shouldn't seem to "favor" any one or another. They should all seem pretty much the same. Do you notice the surface unit wrapping the hose into a coil that it cannot escape? That's a sign of a problem internally. If you are not seeing that I suspect the other jets are pushing the Polaris away from the shallow end. Try hooking it to one of THOSE returns and see if it avoids the deep end...

Carl