They are probably hatching early because your incubator is running warm. Before your next hatch calibrate a thermometer and check that. You will probably have to tweak the temperature down at least a full degree. But this is for next time.
The main reason you want to remove the turner for lockdown is to make clean-up easier. I don’t know what yours looks like but the chicks poop and drag some of that after hatch slime around. If the motor is exposed that could get messy.
Another reason to remove turners is that many have some sharp corners where a chick could possibly catch a foot, wing, or neck. This is one of those things that is highly unlikely to happen but it is possible. I would not worry about this a lot but immediately turn that turner off so it is a lot less likely to trap a chick.
The reason you are told to not open the incubator during lockdown is that it is possible to shrink wrap a chick that has pipped when you do this. This is something that doesn’t happen a lot but it is something that is possible to happen. I did it once so I’m hesitant to casually open the incubator during lockdown. But it happens so rarely that if I have an emergency I open the incubator and take care of the problem. I don’t always have “ideal” situations but sometimes have situations “I deal” with. That’s where you are.
I just noticed your last post. I think you did the right thing. Some people have absolutely no self-control and casually open the incubator during lockdown all the time. I’ll PM Amy and ask her to look at this thread. She has a lot of experience in opening incubators. Maybe she can help boost your confidence.