We have a pebble-tec pool and just got a completely rebuilt navigator. I saw it working in the guys non pebble-tec pool. We try it in ours and it will go for a few minutes or so and then stop or go real slow. We even cleaned the cartridge filters. One thing of note is that the Bottom Collector Manifold is broken in a spot so unfiltered water is getting through, but not sure if this has anything to do with the cleaner.
The suction lever is in the correct spot. What else can I check? There are no obstructions visible.
edit: now it just doesn't go at all.