Ya, I was thinking sanitation as well... but on the flipside... like didn't rinse out the bleach well.

SOme questions:
-how much sugar did you use to prime?
-did you boil the sugar before adding to the soon-to-be beer?
-how did you add it??

I like to boil the sugar with a cup of water, then add that to the bottom of the "bottling jug". THe s-t-b-beer then swirls with the thin sugar syrup and distributes thru the carboy. Also i might drag the bottom of the racking cane/tube once along the bottom of the yeast cake, to make sure some yeasties are suspended (in case of high flocculation yeastie beasties).

hth!

Headspace usually will not make much of a difference unless you are talking like 1/2 filled bottles, but as long as it is the usuall small amount, it does not matter much.

I am thinking that the idea on not rinsing the bottles after sanitization may be the deal, some you rinsed well and they are carbonated, and others had too much bleach solution left in them and it killed the yeast in the beer.