People on this forum have reported excellent hatch rates with humidities varying from below 20% to above 60%. I don't think, from the information given so far, that anyone can be 100% sure that the humidity was too high. HutsonHeritage has not said, and nobody has yet asked, whether the dead chicks were floating in excess liquid, or whether the live chicks hatched were large and soggy. For a very very dry area 65% humidity for the first 18 days might have been just fine. I agree that it is likely that the humidity was too high, but I would state it as no more than that: a likelihood or an opinion, not a certainty.
HutsonHeritage: If you want to figure out your ideal humidity, get a cheap digital kitchen scale and weigh your eggs to determine their moisture loss. It's the most accurate way to figure out what humidity to run your incubations at. Eggs need to lose roughly 13% of their starting weight by the time they get to lockdown, so if you weigh your eggs at the start you can figure out how much they need to lose. I like to weigh mine at days 6 and 12, that gives me a chance to assess the humidity and decide if I need to adjust it up or down...