It was my 1st big set. Id done a few lots of 2 from my own chooks and decided it was a cheaper way to diversify my flock. But new uncalibrated incubator got me. I did open the bator a few times at the end to candle as we had a 25 day hatch...i had 8 fully formed babies. So horrible. I have learnt now thats for sure. I have 12 araucanas and 6 fw marans and 12 mixed to go in tomorrow. Fingers crossed all hiccoughs are done and dusted. I feel terrible
Best you can do is notch it up as ' experience ' . My incubator was 3 degrees lower than it was reading. I keep this article of @Sally Sunshine bookmarked to use as a reference and to troubleshoot.
https://www.backyardchickens.com/a/hatching-eggs-101