Pool Rover Plus stops often

[DMand]

My pool is inground,vinyl, 20X40. I just got the Pool Rover Plus. It came with 2 filter bags. 1 bag was in the unit, so that is the one I used.
Problem is every 5-10 minutes, Rover stops moving. There is a layer of dirt and small leaves in the filter bag but not very much - not even 1/4 full. I wash out the bag, replace it, and the same thing happens every time. I did this 5 more times then it got dark and I gave up.
Should I be using the other bag instead? My pool has small piles of fine dirt and some leaves.

How full should the bag be when the unit stops moving?

Don't know what I am doing wrong. But at this point, it is actually easier to pull out the manual suction vac and hose then to keep pulling the Rover out of the water and cleaning the bag so often.

Any ideas?