There could be many reasons why you have had 50% hatch rates.
1 Shipped eggs have lower hatch rate because of damage to the air cell during shipping.
2. Quality of egg shell
3. Health of the parent birds
4. Temperature during incubation. Should be 37.5 Celsius or equivalent in Fahrenheit
5. Humidity during incubation. Should be 45% day 1-18 then 65% for lockdown.
6. How your eggs are turned during day 1-18. If hand turning at least 3 times per day but
5 is better.
Hope this helps you a little and this is a great link for learning about incubation. https://www.backyardchickens.com/a/hatching-eggs-101
Good luck with your future hatches
A lot depends on what kind if incubator you are using, and what the average humidity is where you live. If you are using a "Styro" humidity is especially deceiving. The instructions tell you to add water in the bottom, but where I live (Kentucky), I dry hatch and do very well with them in the Spring and Summer. TSC sells a thermometer with a hygrometer on it for $2.99. I use that in my Styros. I have 3 GQF Sportman incubators and only use the Styros in a pinch, like in Spring when I am overloaded with Goose eggs.
Another factor with the Styros is that the instructions that come with them have the wrong information if you do not have a fan attachment. They state that the incubating temp should be 99.5..this is correct for a forced air incubator, but a still air incubator should be around 101.5.
Hope I've helped in some small way.
Feather People Farm