I don't think there is one right answer for all of us. From different posts on here, different peope get different results using the same humidity or different humidities work for different people. I don't have a LG so I can't give any advice from experience with them.
What I have been successful with with my 1588 is lower 40's during incubation and mid-60's during lockdown. When they start to hatch the humidity goes up to the mid-80's and things seem to be fine. I do think 35% is way too low. I'm not familiar with the LG but that kind of a drop makes no sense. Did you get the lid back on right when you went into lockdown? Don't ask how I know to ask this.
If you do add a container of water, I'd suggest hot water so the incubator does not have to heat it up before it starts to evaporate. I have shrink-wrapped chicks before by opening the incubator during hatch, but I think the risk of that is a lot higher once they pip. If you are going to do it, do it as soon as possible, before they pip.
Again, I don't know your incubator, but if it is a still air (no fan) I would definitely take the plugs out. The chicks need the oxygen. Mine is forced air and I still take the plugs out, but my 1588 has enough water reservoirs that I can maintain humidity when I close the lid properly.
Good luck!