Try giving the bag a good rinsing - then wash it in the washing machine.

Reload it in the dolphin and I think you'll see a bid diff.

Also - if the bag is wet, I always have trouble getting the dolphin to sink - I usually just tilt it on its side when that happens.

I also always have trouble getting it to climb the walls if there's any slimy residue on the pool sides or bottom since it clogs the filter bag quickly. Also poor climbing after a few hours in a significantly dirty pool.