Why did my crosses not hatch?

[Shleber12]

Ok Here is what happened. We have 1 buff roster and 3 welsummer roosters in with both buff and welsummer hens. We hatch out eggs every years, but this year is the first for crosses. So we just got done hatching out 18 of our 38 eggs. We gave the unhatched eggs a whole extra day to hatch. Heard no peeping and no rocking so I assumed they were duds. I decided to crack the unhatched eggs to see where they were in development. Upon doing this I discovered EVERY SINGLE ONE was fulling developed but had all died. I also found that about have had what looked to be a swollen throat. It didn't matter what color egg they were in. Half were in a buff colored egg and the other half in welsummer eggs. Of those that did not hatch 6 were what I would assume were gonna be dark brown due to the feather coloring. The reason I point out the coloring is because ALL that did hatch are either buff yellow, or just a tad bit darker cream. So in saying all of this I'm wondering if anyone has run into the possibility that maybe the buff has a more dominate gene causing some of the crosses to not be strong enough or maybe just not able to survive in general. We hatch every year and have for about 10 years now. Generally if they are duds they're just not developed. This is the first time for us crossing. I'm hoping maybe someone could shed some light on this.

 

[Poultrybonkers]

sounds like your humidity was to high