Runner duck egg issues

I'm having issues with incubating Runner ducks!

Yesterday was one of my incubators hatching day and in that one I had Apple Silveryards, Magpies, Call and Runner ducks. This is only my second hatch, first of ducks, and I had a pretty good hatch rate with everything but the Runners. The Runners didn't fair so well, they developed normally and were fully formed but died without hatching. They look like maybe they drowned in the egg? Do the Runner ducks have different humidity requirements or something? I love Runners and would love to hatch some out but feeling pretty bad about all the lost wee ones at the moment. Thanks for any advice.

Jenifer