shell may be too hard - not enough humidity! its a balance too wet drowns them , too dry they will die of exhaustion trying to get out. if you see unzipping maybe mist a spray bottle on them.Between 40-65 and the incubator turns eggs. They’re dying in shell around day 20-22
Dont drown them though.
vent open , then vent closed in lockdown , BUT, dependant on humidity levels.
you need a good hydrometer