it happens. When I first started raising babies, I learned a little more with each clutch. You are making progress. Raising rotifers and getting the bubbles just right for the larvae to hatch are tricky tasks.
Possible problems could be too strong of a bubble movement that pummels the larvae, improper food density. Not enough rotifers and they starve. Too many rotifers and the oxygen supply and water quality suffer. Too much phyto in the same water with the rotifers and larvae could foul the water.
Best of luck with the next clutch.