It seems like it may be a humidity problem. Many people hatch at 65%. I wouldn't worry about the humidity when you open the door. Just remember when a broody hatches chicks she usually gets off of the nest for up to 30 minutes daily to eat, drink and poop. I incubate in a cabinet incubator too but I do have vent holes on the back and since your incubator is really meant for reptiles could you drill any holes in it for air circulation?
![](https://www.backyardchickens.com/content/type/61/id/5487438/width/500/height/1000)
![](https://www.backyardchickens.com/content/type/61/id/5494314/width/500/height/1000)