If they are really light then they are dried up. I had the same thing with half my BQ eggs last hatch.
Would you believe I put my BQ eggs in the bator on 6/26 and today I have/had one trying to hatch (zipped part way) and 3 others that pipped? Now I don't know what to do because I didn't up the humidity and I have the egg turner in there. Got it leveled off and turned it off but don't know what to do.