It is expected that you may have some condensation in your incubator during hatching time. If there is not any it does not always mean, there is something wrong or that the incubator is not working.
In a lot of cases condensation can be bad sign and could indicate either that your humidity may be too high or that the location of the incubator is too cool or cold. Condensation when your chicks have started to hatch is normal, but if they have not yet started to hatch and you are noticing excessive amounts of condensation then it could mean the room is too cold or the humidity is too high and would suggest opening the vent and checking the room temperature. Ideally your incubation room wants to be between 18-22°C.
If you are noticing your incubator ‘fogging up’ and only a slight amount of condensation during hatching then don’t worry, this is normal. It is only when you start to see excessive amounts condensation to the point where the incubator is soaking wet that you need to open the vent and let some of that moisture out or check the temperature of the location.